Johannes Justus Rein (1835-1918), a German geographer, stayed in Japan during the period 1874-1875 by order of the Prussian Royal Government. He extensively researched not only the industry and commerce of Japan, which was the main task with which he was entrusted by the government, but also the geography, geology, botany, zoology, and meteorology of Japan, as well as other scientific fields, based upon his own interests. “Dr. J. Rein's Reise in Nippon, 1874,” which we have now translated into Japanese, is his first paper about Japan, and was written mainly from the latter viewpoint. From May to July 1874, he traveled to central Japan along the Tokaido, Nakasendo, Hokurikudo, and Hokkokukaido highways, returning via the Nakasendo highway, in a clockwise round trip through mountainous regions, where he observed the mountains, rivers, plants, animals, climates, and lives of inhabitants along the roads. In this paper, he presents a topographic division of the region, proposing that “the Japanese Snow-ridge Range”—roughly corresponding to the present-day Hida Mountain Range—is the most important mountain range, and mentions its climatic significance. During the trip, he climbed volcanoes such as Mt. Hakusan, Mt. Asama, and Mt. Hakone, and also collected many plant specimens.