An EPC connected between a three phase motor and a battery fixes a voltage of the V phase of the three phase motor to a voltage potential of a positive electrode of the battery. A converter unit is placed for each of the U and W phases of the three phase motor. Each of the converter units has a chopper circuit part and a capacitor. Each of the converter units converts the voltage of the battery to a desired voltage. The voltage of each of V and W phases is adjusted until the voltage of being twice of the voltage of the battery based on the voltage potential at the positive electrode of the battery as a reference voltage. This makes it possible to adjust the absolute value of a line voltage between V and W phases until the voltage of the battery as an upper limit voltage.