To provide a moving direction conversion mechanism for converting a radial movement transferred from a motor to a piston movement in a thrust direction.

A recessed groove 8 is defined inside a rotary cylinder 5 which turns in a state being inscribed in a fixed casing. A slide shaft 6 for piston movement is incorporated in a state being inscribed into the rotary cylinder. When a protrusion 9 is arranged on the outer surface the slide shaft so as to be fitted to the recessed groove of the rotary cylinder, and the turning movement of a motor turns the rotary cylinder, the slide shaft turns together in a radial direction. However, as a guide is mounted on the slide shaft so as to perform a piston motion in a thrust direction, the turning movement transferred from the motor to the rotary cylinder is converted into a piston movement in a thrust direction by means of the slide shaft working.