To provide a hydraulic motor in which the lubricity of sliding parts of pistons disposed in a cylinder block is improved to prevent the motor from being seized and the deterioration of the efficiency of the motor is prevented.

The hydraulic motor 1 includes a case 2 filled with oil, an output shaft 3 stored in the case 2, a cylinder block 4 attached to the output shaft 3 and stored in the case 2, a plurality of cylinder holes 4a formed at the cylinder block 4 about the axis of the cylinder block 4 in the axial direction Y, and pistons 5 slidably disposed in the cylinder holes 4a on inner wall surfaces of the cylinder holes 4a. An oil sump 6 is formed at a portion (X) being the outer peripheral surface of the piston 5 of the hydraulic motor 1 and projected from the cylinder hole 4a and in a slidable contact state with the inner wall surface of the cylinder hole 4a, and in the outer peripheral surface (α) of the piston 5 which faces the inner wall surface near the opening of the cylinder hole when the piston 5 projects mostly from the cylinder hole 4a.