When a vehicle stops in a driving range such as a D-range at low oil temperature such as the initial stage of starting the engine, air-mixed operating oil may be supplied from the second oil passage into the torque converter. In this case, at the release of the lockup clutch in which the second line oil pressure is supplied from the second oil passage to the lockup clutch, the third oil passage is shut off (blocked) to inhibit the discharge of the operating oil. Therefore, regardless of larger pipe passage resistance due to higher viscosity, the operating oil in the torque converter is certainly discharged from the first oil passage through the cooler oil passage to the oil cooler and bubbles in the torque converter is reduced in association of the discharge of the operating oil.