Parking brake system

A parking brake system, comprising:

• a position valve that selectively outputs operational pressure supplied from a hydraulic pressure supplier, to a pressure control valve corresponding to a shift range including a parking range, by operation of a solenoid valve;
• a parking releasing valve that receives an operational force from a solenoid valve, the parking releasing valve that operates at other shift ranges than the parking range, and outputs the operational pressure selectively received from the position valve;
• a main actuator outputting operational force converted from the operational pressure transmitted from the parking releasing valve to release a parking gear, or removing the operational force to restrict the parking gear;
• a sub-actuator that releases the parking gear by providing an operational force to the main actuator when an engine works, and does not provide the operational force to the main actuator when the engine stops;
• a sensor that detects whether the main actuator operates or not and outputs the detected result to a shift control unit;
• and
• a return member that applies a return force to the main actuator to release the parking gear when the operational pressure provided from the parking releasing valve and the operational force provided from the sub-actuator are removed.