To provide an actuator enabling improved flexibility of design of the entire actuator, by improving flexibility of installation of a regulating means for regulating rotation of an output shaft at a predetermined position.

The regulating means 30 is provided with a linear motion converting part 31 converting rotation of a regulating gear 20 into linear motion of a linear motion member 32, with the regulating gear 20 as a rotary body meshing with a second speed reduction gear 12 as a rotary body of a regulation object. The rotation of the output shaft 15 is regulated via the regulating gear 20 by regulating the linear motion of the linear motion member 32.