PURPOSE: To prevent leakage of pressurized medium by controlling the rotation of a motor and the open/close condition of a valve through an operation transmitting means having a coil spring wound over the rotary shaft of the motor such that it can perform and release the accompanying rotation at a small diameter section.

CONSTITUTION: An operation transmitting means 4 has a coil spring 7 wound over the rotary shaft 8 of a motor 5 such that it can perform and release the accompanying rotation at a small diameter section 7a of the coil spring 7. After the rotation of the rotary shaft 8 is started, the coil spring 7 rotates more than half rotation so as to fasten a large diameter section 7b and the side end section 7d of the large diameter section causes the opening operation of a discharge valve 3, thereby the valve does not open freely even if the rotary shaft rotates in the opposite direction thus preventing the leakage of pressurized medium.