A feed screw mechanism including a screwed shaft which moves linearly along with the control shaft, and a rotation spindle which rotates in a circumferential direction. The feed screw mechanism converts a rotational movement of the rotation spindle into a linear movement of the screwed shaft. A protrusion protrudes outwardly from the rotation spindle. An internal thread member engages with an outer wall surface of the rotation spindle. A motor stator generating a magnetic is positioned over the rotation spindle, and is sandwiched between the protrusion and the internal thread member in an axial direction of the rotation spindle.