Korean National Advocate

Joseon Kingdom Appointment Documents (Chōsen-koku Kokushin): Three Royal Letters that Bridged Medieval Japan and Korea

On the rugged island of Tsushima, midway between Kyushu and the Korean Peninsula, there survives a remarkable trio of large paper documents bearing the formal seal of the Joseon court. Known as the Chōsen-koku Kokushin, or "Joseon Kingdom Appointment Documents," these three royal letters were issued in 1477, 1482, and 1503 to the Sōda family, one of the most powerful seafaring clans of medieval Tsushima. Each document conferred a Korean official rank upon a Japanese seafarer, transforming yesterday's pirate captains into today's licensed envoys. Designated an Important Cultural Property of Japan in 1974, this set is the oldest substantial collection of Joseon appointment papers preserved on Japanese soil and offers an extraordinary first-hand window into the diplomacy that ended an age of raids and inaugurated centuries of legitimate cross-strait trade.

What is a "Kokushin"?

The word kokushin (告身, Korean: goshin) refers to a formal letter of appointment issued by the sovereign to a newly invested official. The system originated in Tang-dynasty China and was adopted by the Korean kingdoms; under the Joseon dynasty (1392–1910) it was used as the standard certificate of court rank and office. A kokushin therefore was not a simple commission letter but a tangible token of the recipient's place within the royal administrative order, signed, sealed, and dated according to the Chinese reign-name calendar then in use across East Asia.

What makes the Tsushima examples remarkable is that all three were issued not to Korean subjects but to Japanese mariners — the so-called wajin (倭人) — who had been brought into the Joseon system through a deliberate policy of accommodation. The court's aim was simple: by granting official rank, modest stipends, and trading privileges to influential Japanese leaders, the throne hoped to convert troublesome pirates into peaceful, registered partners.

The Sōda Clan and the Pirate Coast of Tsushima

The recipients of these documents belonged to the orbit of the Sōda (早田) family, a clan of merchant-warriors whose home base lay in the village of Ozaki on Tsushima's deeply indented western shore. From the late fourteenth century the Sōda built a maritime network reaching from Kyushu through the Korean coast to Ming China and as far as the Ryukyu Islands. At its height the clan controlled some seven hundred households across several harbors of Asō Bay, making it the largest single settlement complex recorded on Tsushima in the Korean geographical work Haedong Jegukgi (1471).

The Sōda are best remembered, however, as leaders of the so-called wakō, the Japan-based raiders who plagued the Korean and Chinese coasts during the late fourteenth and early fifteenth centuries. In 1419 the Joseon court launched a punitive expedition known in Japan as the Ōei Invasion, sending more than two hundred warships against Tsushima. Sōda strongholds were among the first targets. Yet within a generation the same clan had reinvented itself as a pillar of the new licensed trade, and it was their descendants — and others like them — who came to receive the very kokushin now preserved as cultural treasures.

The Three Surviving Documents

The set comprises three large single sheets of strong, hand-laid Korean mulberry paper (kōshi). Each was inscribed in formal classical Chinese, the diplomatic language of the day, and dated using the Ming-era reign names recognized by Joseon at the time.

The first document, dated the seventeenth day of the ninth month of Chenghua 13 (1477), measures approximately 98.9 by 85.4 centimeters and was issued to an unnamed wajin recipient. The second, dated the third month of Chenghua 18 (1482), measures roughly 98.0 by 79.8 centimeters and was issued to a wajin recorded as Hikosanbora. The third, dated the third month of Hongzhi 16 (1503), measures about 106.6 by 80.6 centimeters and was issued to a wajin recorded as Hikoira. The names are Chinese-character transliterations of Japanese sounds, a common convention in cross-strait correspondence of the period.

Although the three letters are addressed to different individuals, they are unified by their shared origin in the Sōda household archive and their shared purpose: each conferred Korean official rank on a Japanese mariner, granting in return the right to send licensed trading vessels to designated Korean ports.

Why These Documents Were Designated an Important Cultural Property

The Japanese government formally designated the Chōsen-koku Kokushin an Important Cultural Property on June 8, 1974. The reasoning rests on three pillars of value.

First is rarity. While individual Joseon-period appointment documents survive in scattered Korean collections, sets of three issued to Japanese recipients are exceptional. Among kokushin preserved in Japan, this group is the oldest substantial assemblage to come down to us.

Second is documentary value. The letters are primary sources for the so-called jushokujin system, by which the Joseon throne enrolled influential Japanese leaders into its bureaucratic hierarchy. Modern historians of medieval East Asian diplomacy depend on such physical evidence to understand how rank, trade, and political loyalty were negotiated across the strait.

Third is material integrity. Each document is a single, generously sized sheet of Korean mulberry paper, and the calligraphy, formal layout, and seals remain legible after more than five centuries. They survive not as fragments but as complete certificates, allowing scholars to study every aspect of fifteenth- and sixteenth-century Joseon diplomatic protocol.

Highlights and Points of Interest

Visitors who have the opportunity to view the documents in person — typically during special exhibitions — will notice several striking features. The sheer scale of the paper is the first surprise: at roughly a meter on each side, these are not pocket commissions but ceremonial declarations meant to impress. The brushwork is the polished hand of a Joseon court scribe, while the formal Chinese phrasing reflects the shared classical culture that linked literate elites across East Asia regardless of language.

Equally fascinating are the Japanese names rendered phonetically in Chinese characters — Hikosanbora, Hikoira — small linguistic bridges between two worlds. And for the careful observer, the dates themselves tell a story: 1477, 1482, 1503, three moments spanning a generation in which an old pattern of coastal raiding was being slowly rewritten as a system of licensed trade, document by document, seal by seal.

Visiting and Where to See Them

The three documents are privately owned but have long been entrusted to public institutions in Tsushima for safekeeping and study. Historically they were associated with the Nagasaki Prefectural Museum of History and Folklore in the town of Izuhara, which served Tsushima for decades from 1977. The functions of that museum have since been reorganized, with exhibition activities largely transferred to the modern Tsushima Museum (Tsushima Hakubutsukan), opened in 2022 in central Izuhara, while research and conservation are based at the Nagasaki Prefectural Tsushima Center for Historical Research.

Because the documents are extremely fragile, they are not on permanent display. Travelers hoping to see them should check the special-exhibition schedule of the Tsushima Museum or the Tsushima Center for Historical Research before planning a visit. Even when the originals are not on show, the museums offer rich permanent displays on the diplomatic history of Tsushima — including the famous Tsushima Sō Family Documents — that place the kokushin in their proper context.

Around Izuhara: Exploring the Borderland

Izuhara, the historical capital of Tsushima, repays the traveler with a remarkable concentration of border-history sites. Within easy walking distance of the museums you will find Kaneishi Castle Garden, a designated Place of Scenic Beauty associated with the Sō family who ruled Tsushima for centuries, and the Sō-family graveyard at Banshōin Temple, where over a hundred lords and ladies of the clan rest beneath towering cedars. The Kōraimon (Korea Gate), a reconstructed entrance from the former Sajikihara Castle, stands nearby as a reminder of the island's enduring ties to the peninsula.

Travelers with more time can venture out to Kaneda Castle, a special national historic site on Mount Jōyama whose seventh-century stone walls were built to defend Japan against invasion from the continent — a striking counterpoint to the diplomatic documents that, eight centuries later, would help replace conflict with commerce. The Watatsumi Shrine on the western coast and the dramatic ria coastline of Asō Bay round out a visit to one of Japan's most evocative borderlands.