The direction and intensity of magnetic polarization of Tertiary sediments and volcanic rocks in various localities in Japan were measured. Samples were collected from Upper Miocene to the recent beds in Kanto, Toyama, and Kinki districts. A series of samples of sedimentary strata in Kanto, ranging from the lowest bed of Upper Miocene to the uppermost layer of Pleistocene, were examined especially in detail. The declination of magnetic polarization of the whole section, more than 4,000 meters in thickness, is nearly the same as that of the present earth's magnetic field, while the inclination gradually decreases from the mean value of 25° in Miocene to 50° in Pleistocene beds.The reverse polarization was found only in the cases of pyroclastic (volcanic) sediments in the upper part of Upper Neogene and volcanic lavas of the same geological age in Kinki distric