Abstract: A rotary drive apparatus includes a housing having a housing hole defined therein, a cylindrical rotor being disposed in the housing hole, a working fluid passage through which a working fluid for applying a fluid pressure to one end face of the rotor flows, a motion limiting unit configured to limit motion of the rotor toward another end thereof, and an output shaft configured to extract rotary power of the rotor out of the rotary drive apparatus. A predetermined gap for the working fluid to flow therethrough is created between an outer circumferential surface of the rotor and a wall surface defining the housing hole.