The above-described electric power converter steps up or steps down electric power in parallel with the two batteries at the time of the parallel connection (parallel mode). Step-up/step-down operation is controlled via a PWM signal indicating a duty ratio to each of step-up/step-down circuits. The electric power converter described in JP 2013-013234 A has such a circuit configuration that switching elements are shared between the two step-up/step-down circuits, so each of the switching elements operates in accordance with the logical addition of PWM signals of both.

By utilizing the above operation characteristics of the switching elements, the phases of the PWM signals are shifted from each other in JP 2013-013234 A to reduce a loss that arises in the switching elements. That is, as shown in FIG. 17C, an edge-alignment phase shift is carried out. The edge-alignment phase shift is to shift one or both of the phases of the PWM signals PWM1, PWM2 such that the falling edge of an on period of the PWM signal PWM1 is brought into coincidence (connected) with the rising edge of an on period of the PWM signal PWM2. Thus, the number of times of switching (indicated by the broken line) is reduced as compared to the PWM signal shown in FIG. 17A, with the result that a switching loss is reduced. Because the overlap (hatched portion) of the on periods of the PWM signals PWM1, PWM2 as shown in FIG. 17B disappears, a steady loss (overlap loss) due to an increase in current resulting from the overlap is resolved.