To positively accumulate pressure in an emergency accumulator of a hydraulic booster.
A charging valve 100 of an accumulator 73 is composed of a first valve 102 and a second valve 104. The first valve 102 is provided with a throttle part 110e for throttling a passage 106 for feeding operating fluid from a pump 35 to a hydraulic booster so as to generate differential pressure, a pressure receiving part 110g receiving accumulator pressure to actuate the first valve 102, and a chamber 126 into which accumulator pressure is led at the time of the first valve 102 being actuated. The second valve 104 is provided with a pressure receiving part 136e receiving accumulator pressure to actuate the second valve 104, and switching parts 136f, 160 for communicating the chamber 126 of the first valve 102 and a reservoir 37 and cutting off communication between them. A check valve 120 is opened by the differential pressure of the throttle part 110e to accumulate pressure in the accumulator 73, and when this pressure reaches the specified value, the second valve 104 is actuated to close the chamber 126. The first valve 102 is then actuated to lead pressure into the chamber 126, and the first valve 102 is held in the operating state.