An actuator includes: a case; a rod housed in the case, a tip of the rod protruding out of the case from an opening; a motor housed in the case; and a moving mechanism housed in the case and driven by the motor to move the rod in an axial direction. The moving mechanism includes an annular member through which the rod is inserted, the rod has a male thread part on an outer circumference, the annular member has a female thread part on an inner circumference, the rod moves in the axial direction according to rotation of the annular member, the case has a restraining part more toward the tip than the annular member, the rod has a notch extending in the axial direction in a part of a circumferential direction, and radial displacement of the rod is restrained by contact of the notch with the restraining part.