PURPOSE: To improve the reliability, safety and the like by supplying oil pressure to a braking mechanism for certainly releasing a brake even if a specific command pressure is not generated by a solenoid switching valve because of failures.

CONSTITUTION: A manual switching valve 31 is provided between a solenoid switching valve 20 and a parking brake 21, and the parking brake 21 is selectively connected to the solenoid switching valve 20 or a pilot oil pressure source 9. In any abnormal case where specific command pressure is not generated from the solenoid switching valve 20 because of failures of electric system like a pressure sensor 16 or a control unit 18, the discharge pressure from the pilot oil pressure source 9 is supplied to the parking brake 21, moreover the brake can be released by switching the position of the manual switching valve 31 to an abnormal position B from a normal position A.