An actuator having an output axis which is moved linearly by a rotatory force, and a boss for holding the above-mentioned output axis in such a way that the output axis can move linearly includes a connecting member for propagating the linear motion of the above-mentioned output axis to an external device. The above-mentioned connecting member is comprised of a joint connected to the above-mentioned output axis, and a link plate having an end rotatably connected to the above-mentioned joint, and another end rotatably connected to the external device. A mechanism for preventing rotation of the above-mentioned output axis is constructed of only a connecting portion for connecting the above-mentioned joint, the above-mentioned link plate, and the above-mentioned external device to one another.