Converters (6-1, 6-2) are connected in parallel with each other to a pair of electric power lines (MPL, MNL). When required electric power required by a drive force generation unit (2) is not more than a threshold value, a converter ECU (30) causes a voltage converting operation of one of the converters (6-1, 6-2) that is associated with a power storage device of a higher output voltage to perform voltage converting operation, and causes the voltage converting operation of the other converter to be stopped, based on output voltages of the power storage devices (4-1, 4-2) detected by output voltage detection units (12-1, 12-2). The first power storage device (4-1) and the second power storage device (4-2) are configured so that one of the power storage devices has a higher power supply voltage by a predetermined value than the power supply voltage of the other power storage device. The predetermined value is defined based on errors which may be included in detected values of the output voltage detection units (12-1, 12-2).