The nickname "Green Tuff" had been used by Japanese geologists for the Miocene volcanic complex which is characteristic to the inner zone of Japan. However, the area now called the Green Tuff region in Japan is enlarged as shown in Fig. 1. This area is one of the most important mining provinces of Japan in both of metal and oil. In this article, outline of the geological history in this region is explained, attaching importance to northeastern Japan, especially to the Akita district. In the Akita district, the Miocene sediments are stratigraphically divided into seven stages, and they are roughly enumerated as shown in the following table :