A rotary actuator for a shift-by-wire system of a vehicle includes a motor with a motor shaft, an output shaft disposed in parallel with the motor shaft, a speed-reducing mechanism configured to reduce a rotational speed of the motor and transmit the rotation of the motor to the output shaft, and a case housing the motor and the speed-reducing mechanism. The speed-reducing mechanism includes a first speed-reducing portion including a ring gear and a sun gear, and a second speed reducing portion including a drive gear and a driven gear. The drive gear and the driven gear are coaxially disposed with the motor shaft and the output shaft, respectively, to serve as parallel shafts type gears. The drive gear is disposed between the motor and the first speed-reducing portion in an axial direction of the motor.