To improve the energy efficiency while eliminating the useless circulation of oil so as to restrict the heat generation by providing a clutch cylinder with a hydrostatic system directly connected to a hydraulic pressure generating cylinder type electric pump.

A transmission case 1 is connected to an engine, and the power from the engine is transmitted to epicyclic gear trains 3, 4 through a torque converter 2 for shift change, and transmitted to a final gear and tires from a output shaft 5. Multi-disc clutches 6, 6a and a band brake 7 are connected to the epicyclic gear trains 3, 4, and closed and released at need so as to obtain the predetermined change gear ratio. A clutch piston 8 and a brake piston 9 for fastening the multi-disc clutches 6, 6a and the band brake 7 are connected to a separate motor-driven hydraulic pump 13 through a direct hydraulic circuit 12, and the motor-driver hydraulic pumps 13 are maintained at various pump values. With this structure, a clutch after fastening the clutch or the brake oil pressure can be maintained without supplying the energy from outside.