PURPOSE: To cover a wide range of running conditions with a motor having a low rated output and realize a light weight and small size motor by changing quantity of circulating oil in accordance with heat generation of motor, keeping adequae quantity of oil for cooling a motor coil and effectively cooling the coil according to the output conditions of motor.

CONSTITUTION: A driving apparatus is of an in-board type comprising a motor 1, a deceleration unit 2 coupled with the motor 1 and a case 3 for accommodating these elements. For the purpose of cooling the motor 1, an oil circulating means 6 consisting of an oil path and an oil pump 61 provided at the outside and inside of the case 3 and a cooling means 7 for cooling the circulating oil through the heat exchange. The oil circulating means 6 is provided with an oil pump motor 6A for changing quantity of circulating oil in accordance with heat generation of motor 1. Usually, the oil pump 61 is gear-driven for the oil circulation and the driving method is switched to the drive by the oil pump motor 6A in such a case that oil temperature is high but the number of rotations of motor 1 is low.