Process of the tectonic rotation related to Japan Sea opening is viewed from tilt-corrected paleomagnetic data obtained from the Early to Middle Miocene sequence in the Yatsuo area on the Japan Sea coast, eastern part of southwest Japan. Progressive demagnetization experiments have been executed on samples obtained from two routes along the Yamada and Wada Rivers, and successfully isolated stable primary magnetic components in 16 sites. Together with data of previous studies, tilt-corrected reliable paleomagnetic directions comprising 10 normal and 27 reversed polarity sites of the Yatsuo Group on accurate stratigraphic positions show systematic temporal variation of easterly deflection in declinations. On the basis of our presented magnetostratigraphy, Yatsuo Group is assigned from the late Early to early Middle Miocene. Significant stage of rotation as much as 30 degrees is specified during late Early Miocene between a period of active volcanism and subsequent period of marine transgression. We suggest that the Japan Sea opening event had a final phase of rapid rotation around the late Early Miocene, which seems to have caused marine transgression in relation to remarkable subsidence along the Japan Sea coast.