A hydraulic device for operating a clutch in an industrial vehicle having a transmission comprising shift changeable gears and manually operated shift levers. Gear actuating hydraulic boosters are provided for hydraulically actuating the shift changeable gears, and the clutch is actuated by a clutch cylinder. The hydraulic device comprises a clutch circuit extending between a hydraulic pump and the clutch cylinder, and a booster circuit extending between the hydraulic pump and the boosters. A gate valve is arranged in the clutch circuit and is movable in response to pressure of hydraulic oil in the booster circuit, so that the normally closed gate valve is opened when the manually operable shift levers are operated. Also, a pressure control circuit is branched from the clutch circuit and again branched into parallel third and fourth hydraulic circuits. A forward and reverse gate valve and a speed change gate valve are arranged in the third and fourth hydraulic circuits, respectively. A check valve and a first accumulator are arranged in the third hydraulic circuit and a second accumulator is arranged in the second hydraulic circuit upstream of the second gate valve for controlling the use of pressure applied to the clutch cylinder.