A piston motor includes a bush in the form of a curved plate held in sliding contact with a back surface of a tiltable swash plate, a supply/discharge passage formed on the casing including a swash plate port formed on the swash plate and open on the back surface of the swash plate and a bush port penetrating through the bush and provided from a piston to the swash plate, and an elastic ring interposed between the casing and the bush and surrounding an opening end of the bush port.