matter is removed from oil strainer 720 vane pump 700 develops a hydraulic pressure from the oil supplied thereto and supplies the hydraulic pressure to control valve unit 720 control valve unit 720 adjusts the hydraulic pressure of the oil and supplies the working oil to each device oil cooler 730 sucks the oil which is not supplied to each device and the oil stored in oil pan 740 the sucked oil is supplied to the lubricating oil chamber the oil in the lubricating oil chamber is cooled by means of the coolant in the coolant chamber adjoined to the lubricating oil chamber via a partitioning wall and thereafter the foreign matter in the lubricating oil filter 750 installed on filter inserting portion 124 b of oil cooler 730 is removed and supplied to each device torque converter 200 augments the torque transmitted from the engine during a low vehicle speed and engages the lock up clutch during the high vehicle speed during a high vehicle speed to transmit the driving force from the engine to forward and backward switching mechanism 300 in forward and backward switching mechanism 300 the inputted revolution is directly outputted with the sun gear and ring gear integrally engaged by means of the forward clutch during the forward travel on the other hand during the backward run of the vehicle the backward brake fixes the carrier of forward and backward switching mechanism 300 to second housing 120 so.