Hydraulic drive device that converts pressure energy of hydraulic oil into rotational motion. Used for machine tool spindle drives, injection molding machine screw rotation, press machine rotary tables, and construction machinery swing devices. Available in gear motor, vane motor, and piston motor types, supporting wide specifications from high torque low-speed to high-speed rotation. Unlike hydraulic cylinders, provides continuous rotational motion with high power density and precise speed control compared to electric motors. Selected based on mounting flange, output shaft diameter, maximum operating pressure, and displacement specifications.