PURPOSE: To prevent beforehand a bad operation such as an operation in which a changeover operation from a second state to a first state can not be carried out because of the leak of operation oil, by deciding the rear end position of the spring of a pressure governing valve by means of the second changeover portion of a changeover valve.

CONSTITUTION: Even if operation oil leaks out of a first changeover portion 2PA and enters into a chamber 22a, this operation coil passes a cutout portion 22b from the chamber 22a inside and it discharged into a drain portion 35. As a result, the chamber 22a inside is kept at zero pressure at all times, and in a case in which a second changeover portion 29B is operated to the separation inside from the rear end of a spring 1Pb, from a state in which high second set pressure is set, the rear end of the spring 19b follows the second changeover portion 2PB without being separated, and returns to a first state surely. In addition, by providing the cutout portion 22b on the inner surface of a case 22, the position of the cutout portion 22b is fixed at all times without relation to the phase of the spool 29 of a changeover valve 24, and the operation oil in the chamber 22a is discharged into the drain portion 35 surely at all time.