PURPOSE: To obtain a quick engagement of a clutch by controlling the operating pressure of a clutch cylinder at the time of starting a vehicle by filling two accumulators with pressure to realize a shockless engagement of the clutch, and controlling the operating pressure by filling one accumulator with pressure.

CONSTITUTION: A back and forth shifting shift booster 5 and a speed changing shift booster 6 are connected in series with a booster circuit 4 connected to a hydraulic pump 1, and a clutch cylinder 21 is connected through an inching valve 7 to a clutch circuit 8 branched by a flow dividing valve 3. Further, an operating gate valve 15 capable of being switched to an open position by booster operating pressure, and back and forth moving- and speed changing gate valves 16, 17 for releasing the clutch pressure into a tank only at the time of neutral, are provided to a clutch pressure control circuit 13 branched from the clutch circuit 8. Then, a first accumulator 18 for controlling the increase in clutch pressure at the time of starting a vehicle and a second accumulator 19 for controlling the increase in clutch pressure at the time of starting and speed changing are provided.