Nonaka Kofun is a square mounded tomb located to the north side of the round rear part of Hakayama Kofun . Given its position, this tomb is considered to be related to Hakayama Kofun as a satellite tomb.
The mound length is 37 m, and its height is 5 m.
The 1964 excavation of the top of the mound revealed that it contained a row of at least five wooden boxes, and in these were found eleven pieces of iron cuirasses, eight iron helmets, and three leather helmets. There were also large quantities of iron weapons, such as single-edged and double-edged swords and arrowheads; iron ingots used as raw material for iron implements; a stone mortar and pestle set; and stoneware from the Korean peninsula.
Both cylindrical and representational haniwa have been excavated from the mound and the moat.
The construction period dates to the second half of the 5th century.