Abstract: In a method of operating an electric motor which drives an auxiliary oil pump for supplying a hydraulic pressure of an ATF to a transmission, only at an idle stop of an engine via a rotation shaft pivotally supported by ball bearings, the electric motor is rotated at a very low speed or in an intermittent manner when an automobile is traveling and the auxiliary oil pump is not used. According to the configuration, the electric motor is slightly rotated during when the automobile is traveling, whereby impressions are prevented from being formed on the ball bearings.