Mid-Cretaceous ammonoids, Euhystrichoceras nicaisei, Mantelliceras japonicum, and Hypostlingoceras japonicum were collected from float rocks probably derived from the middle part of the Miyanohara Formation in the Sakawa area, Shikoku, southwestern Japan. Although it has been suggested that the stratigraphic correlation of this formation based mainly on bivalves such as trigoniids needs to be reexamined, the occurrence of these ammonoids confirms that the middle part of the Miyanohara Formation is correlated to the lower Cenomanian. The results of this study support the suggestion that the shallow marine deposits of the mid-Cretaceous that contain similar molluscan faunas are widely distributed throughout the northwestern Pacific region.