A control device stores, as a dead time Td, a period from a point of time of a switching-off operation of an inverter to a point of time when an inverter output voltage becomes lower than a control target value “0”. In overmodulation PWM control over the inverter, the control device performs the switching-off operation at a time t1, and thereafter starts a switching-on operation at a time t2 with passage of dead time Td read from a memory. With the setting of dead time Td, the inverter output voltage becomes lower than the control target value “0” at time t2 at which the switching-off operation is started. Hence, the inverter output voltage just after the switching-on operation is less likely to be affected by surge voltage during the switching-off operation, whereby the peak value of the inverter output voltage is made small.