To provide a bathtub cleaning device which ultrasonically and automatically cleans the inner surface of a bathtub, and can be manufactured at a low cost in a simple structure.

This bathtub cleaning device is provided with a casing body 2 designed to float on the water surface, a screw 3 which generates propelling power to push the casing body 2 forward on the water surface, and an ultrasonic element 5 installed on a side wall 2b of the casing body 2. Since the casing body 2 is formed to obtain propelling power toward the bathtub inner surface from the screw 3, while it is moved around along the inner surface of a bathtub with the 2b side facing the bathtub inner surface, the ultrasonic element 5 cleans the bathtub surface in contact.