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The Myoko volcano, one of the stratovolcanoes in the northern part of the Fossa Magna, Central Japan, has the complicated history (Table 1).The last activity of the Myoko volcano is called the IV stage, and is divided into precaldera, caldera, and central cone substages. The strata formed during this stage are collectively called the Myokosan group which consists of lavas, pyroclastic flow deposits, pyroclastic fall deposits, volcanic mud flow deposits, and lake deposits. They are described in detail and their stratigraphic relations are tabulated in Table 2 and Fig. 4.The rocks of the essential eruptives are basalt, pyroxene andesite and hornblende andesite. They change from basalt to pyroxene andesite and hornblende andesite keeping step with the eruptive order. Quantitatively, the hornblende andesite is predominant.