A new partial skeleton consisting of a left mandible and five caudal vertebrae, OMNH-QV 282 from the Osaka Group (Middle Pleistocene, about 0.3 million years ago) of Osaka City is reported as the first cetacean record from the group. The skeleton is identified as Balaenopteridae gen. et sp. indet. based on the combination of mandibular characters, such as having a small mandibular foramen, reflected neck in dorsal view and lack of a satellite process of the mandible. OMNH-QV 282 expands diversity for the local fauna, and also adds evidence for the existence of large-sized balaenopterids from a poorly known epoch, the Middle Pleistocene.