To provide an actuator at low cost.

A driving unit inside a casing is formed of a cylindrical coil and an inside rotor, and a shaft 32 is inserted into the rotor. A male screw 41 of the peripheral surface of the shaft 32 is screwed to a female screw of the inner peripheral surface of the rotor to convert the revolution of the rotor to the linear movement of the shaft 32. A terminal part of the male screw 41 of the shaft 32 is formed with an abutment surface 63 standing in relation to a tangent 62 of a screw root 61 of the male screw 41 so that the abutment surface can abut on a thread of the female screw of the rotor. Standing angle α of the abutment surface 63 in relation to the tangent 62 of the screw root 61 is set at 45 degree or more.