To provide a hydraulic motor capable of surely fixing a support shaft for supporting planetary gears to a motor easing at a low cost without increasing the size of the motor.

This hydraulic motor 1 rotates a rotary drum 3 after reducing the rotating speed of an output shaft 5 through a planetary gear speed reducer 4. The support shaft 17 for pivotally supporting the planetary gears 14 of the planetary gear speed reducer 4 is fixed to the motor easing 6. A fitted recess 14 for fitting the support shaft 17 thereto is formed in the motor easing 6, a shaft side locking groove 20 is formed at the tip part 17a of the support shaft 17 around all the periphery thereof, and a recess side locking groove 21 is formed on the inner peripheral part of the fitted recess 24 around all the periphery thereof. With a C-shaped elastic locking ring 22 fitted into the shaft side locking groove 20, the tip part 17a of the support shaft 17 is inserted into the fitted recess 24. When the shaft side locking groove 20 is aligned with the recess side locking groove 21, the locking ring 22 is fitted elastically to the recess side locking groove 21.