To provide a rotational angle limiting mechanism of a rotary valve for easily changing the upper limit or the lower limit of the opening angle of a valve element of the rotary valve as necessary, and an actuator having the rotational angle limiting mechanism.

In the actuator having a rotary shaft having a fitting part to a valve shaft of the rotary valve at a lower end thereof and a rotating mechanism to rotate the rotary shaft, a cam is attachably/detachably fitted to a lower end of the rotary shaft from an open port formed in a lower surface of the actuator, and a stopper bolt which collides with a specified part on a circumferential edge of the cam to restrict the rotation of the cam is added to the actuator.