In an electric actuator, one end portion of a return spring is hooked to a first slit formed in a radially outer guide of an output gear, so that the return spring is twisted for a predetermined angle that is slightly smaller than an initial set angle. A tilted slit portion is formed at an opening of a second slit that is formed in a covering wall of a spring installation member to twist the return spring to a predetermined initial set angle. Thereby, simultaneously with assembling of a valve shaft to the output gear, the return spring is twisted for the initial set angle. Thus, an assembling work of the electric actuator can be simplified.