Mt. Hoei (Hoei-zan) is a protuberance on the southeastern flank of the Fuji volcano, Japan. The lateral cone was formed during the Hoei eruption in AD 1707. However, the geological map of the Fuji volcano assigns the material of the protuberance to an older unit in the Hoshiyama Stage (100 to 17 ka); this is because the Akaiwa deposits around the summit have been altered in the same manner as rocks in the Hoshiyama Stage. This assignment has led to a model, unique in the context of modern volcanology, in which Mt. Hoei is an uplifted bulge caused by the intrusion of degassed magma that occurred at the time of the eruption; it thus led us to reinvestigate the geology of Mt. Hoei for the first time since Tsuya (1955). In addition to a geological survey, we obtained paleomagnetic directions from the Akaiwa and fallout deposits in the Goten-niwa erosional valley at the base of Mt. Hoei and compared the former with directions from the spatter cone that formed in the first Hoei crater during the final stage of the Hoei eruption. All the directions agreed well with each other and the archeomagnetic directions reported as corresponding to AD 1707, clearly indicating that the Akaiwa is not a part of the Hoshiyama Stage. We also performed petrographic and whole-rock chemical analyses of the deposits and found a gradual upward compositional change from dacite to basalt corresponding to the distal tephrostratigraphic units Ho-I to Ho-IV. This result shows that the Akaiwa deposits corresponded to the rocks of unit Ho-III, and both paleomagnetic and petrologic investigations strongly suggest that the former formed contemporaneously with the eruption. Therefore, the protuberance is not a bulge caused by the magmatic intrusion but a pyroclastic cone from the Hoei eruption.