Kanizawa Tumulus is a circular tomb of the early Tumulus period (around the 4th century), which was located in Shibazaki-machi, Takasaki, Gunma. While the burial chamber inside the tomb is assumed to be of nendokaku type (clay type), the details of the excavation conditions are unknown. The excavated artifacts include 4 bronze mirrors, 2 iron axes in rectangular shape, 1 iron chisel, 1 iron sword and 9 pieces of unglazed reddish brown earthenware. Among them, the sankakubuchi-shishinshiju-kyo (a type of bronze mirror) has the so-called doko layout (patterns are arranged so that they can be all looked at from one direction) and an inscription (「□始元年陳是作鏡…」) is cast clockwise in the outer section. Mirrors cast out of the same mold as this one include those excavated from the Takeshima Tomb located in Shinnanyo-shi, Yamaguchi and the Morio Tomb in Toyooka-shi, Hyogo. From the inscriptions on these mirrors, it was found that they were created in 240 in Wei during the Three Kingdom period in China. According to "Gishiwajinden (the oldest chronicled reference to Japan)," Wei granted gold and silk fabrics, 錦罽 (brocade), swords and mirrors to Japan in 240. This sankakubuchi-shishinshiju-kyo bears the inscription of the year 240 and is the most important material for the study of Queen Himiko's period. It is a very valuable material not only because artifacts excavated from tumuli that bear the inscription of their creation years are very rare, but also because this mirror constitutes an integral part of a set of valuable materials including other burial accessories that were excavated at the same time.