Yamamoto Rock Machine (Former Yamamoto Iron Works)

Yamamoto Rock Machine (Former Yamamoto Iron Works): A Rock Drill Maker's Works in Tojo

Yamamoto Rock Machine (Former Yamamoto Iron Works) (ヤマモトロックマシン（旧山本鉄工所）) is a group of factory, office and company housing buildings in Tojo-cho (東城町, Tōjō-chō), Shobara City, Hiroshima Prefecture, where ten wooden buildings erected from 1934 onward are listed as Registered Tangible Cultural Properties. Eight of them were registered on 25 February 2016, and the former head office and the former research laboratory joined the list on 3 December 2024.

The owner is still the company that built them. Most of the workshops remain in production, turning out the percussive drills used to bore blast holes in tunnels and quarries. Across the road to the south, the old company dormitories tell a different story: empty for decades, they have been cleaned out and repaired by local volunteers and now host occasional open days, concerts and workshops. A working factory on one side of the street and a revived residential quarter on the other: the two halves together show how one prewar company organized work, housing and training in a small mountain town.

This page covers what the ten buildings share: the company's history, the layout of the site, how the registrations came about, and how to reach Tojo. Each building has its own page for construction details and what to look for.

From Foundry to Rock Drills: The History of Yamamoto Rock Machine

The business began in February 1915, when Yamamoto Shuichi opened a small ironworks in Tojo. According to the company's own history it first cast household ironware, then added machine tools and moved into repairing and building engines and sawmill machinery.

The turning point came from hydroelectric construction nearby. From the mid-1920s into the early 1930s the Taishakugawa dam and the Nariwa River power station were built in the surrounding mountains, and contractors brought in large numbers of imported rock drills. Yamamoto took on their repair and the supply of spare parts, and from there set out to manufacture rock drills in Japan, which at the time relied almost entirely on foreign machines. The company says it invited an engineer from Germany to learn heat treatment. A rock drill hammers against stone without pause, and how its steel parts are hardened largely decides how long it lasts.

The buildings on the site track that growth. The First Factory went up in 1934; the Second Factory and the dormitory family building followed in 1937, with the finishing factory and the dining hall built around the same time. The youth school dates from about 1938, the lavatory building from about 1939 and the single employees' dormitory from about 1941. The former head office and research laboratory are recorded as prewar Showa-period buildings. In February 1939 the firm was incorporated as Yamamoto Iron Works Co., Ltd. with capital of 1.3 million yen and a head office in Marunouchi, Tokyo.

During the war the plant came under military management and also made aircraft parts for the navy. After 1945 it shifted from coal-mine drills to machines for dams, roads and tunnels. The company adopted the name Yamamoto Rock Machine Co., Ltd. in 1996 and marked its centenary in 2015.

How the Yamamoto Rock Machine Site Is Laid Out

The ten buildings sit in two blocks on either side of an east-west road. Even the addresses differ: the northern block is in Shimomachi, Tojo, and the southern block in Shincho, Kawanishi.

North of the road: the factories and the old head office

At the center stands the First Factory, 78 meters long. The Second Factory meets it at right angles to the north, the finishing factory runs parallel on its east side, and the small lavatory building sits parallel to the west. At the western edge of the block, the former head office and main house faces west onto Shinmachi-suji, one of Tojo's old streets, with the former research laboratory directly behind it to the east. The public face on the street and the production sheds behind it are arranged exactly as the business worked.

South of the road: the dormitories and the youth school

The Agency for Cultural Affairs describes the dormitory buildings as standing across the road south of the factories. The three-story family building is on the west, the 59-meter single employees' building on the east, and the dining and recreation building between them, all with the same clipped-gable roofs. The youth school, where the company trained its apprentice machinists, shares the Kawanishi address.

To see everything from outside, start on Shinmachi-suji in front of the old head office, walk east along the road past the factory roofs, and finish on the south side facing the dormitories. The whole circuit is well under a kilometer.

How Yamamoto Rock Machine Came to Be Registered

The first eight buildings were entered on the national register on 25 February 2016, in the 83rd round of registrations: the First and Second Factories, the finishing factory, the youth school, the lavatory building, and the three dormitory buildings. Their registration numbers run consecutively from 34-0156 to 34-0163, and all were registered for contributing to the historic landscape of the country.

The Council for Cultural Affairs recommended two more on 19 July 2024, and on 3 December 2024 the former head office and main house (34-0310) and the former research laboratory (34-0311) were added. The laboratory is the only one of the ten registered as a model of design rather than for its contribution to the landscape.

Behind the registration lies a volunteer effort. According to the group working to preserve the dormitories, nobody had lived in them since the 1970s. From 2012 local residents, a neighborhood improvement association and architects began meeting to discuss their future, and in 2014 they held a mass clean-up and the first public opening. In 2019 a crowdfunding campaign raised more than its target toward repairing the family building's roof.

Getting to Yamamoto Rock Machine and Visiting

The nearest station is Tojo on the JR Geibi Line. The factory block is about 1 kilometer south of the station, roughly a 15-minute walk. Trains on this part of the line are infrequent, so check the timetable before you go. By car, Tojo Interchange on the Chugoku Expressway is about 1 kilometer away; the streets in the old town are narrow.

All the buildings are on private land and there is no regular opening. The factories are an operating plant with no reception or visitor route. You can see the exteriors from the surrounding public roads, but do not enter the grounds or buildings without permission, and take photographs from the street.

The interiors can be seen only during open days and events organized by the company or the preservation group. Tours, workshops and small concerts have been held at the old dormitories and the former head office at irregular intervals, not on a fixed annual date. If you are planning a trip around a visit inside, contact the company or Shobara City's tourism office for the latest schedule.

The Name Yamamoto Rock Machine

In Japanese the name is read Yamamoto Rokku Mashin (kyū Yamamoto Tekkōsho). The official name of each property pairs the current company name with the former one in brackets, and all ten share it. When the firm was incorporated in 1939 it wrote its name with the older character form, 山本鐵工所. The "Rock" in Yamamoto Rock Machine refers to rock drills, not locks.