A rotary actuator includes a rotation shaft rotatably driven by a motor, an internal gear provided on an outer side of the rotation shaft in a radial direction of the rotation shaft, a rotation output section provided between the rotation shaft and the internal gear in the radial direction to reduce a rotation speed outputted from the rotation shaft and to output a power in conjunction with the internal gear, a cylindrical housing portion fixed to the internal gear, and an attachment member integrated with an outer wall of the housing portion. The internal gear has a protrusion protruding from an outer wall of the internal gear, and the housing portion has a recess into which the protrusion is inserted. The attachment member has an attachment hole that is different from the recess in position in a circumferential direction of the housing portion.