The upper-arm and lower-arm switching elements are complementarily turned on or off. That is, when the lower-arm switching element is in the on state, the upper-arm switching element is in the off state. Conversely, when the upper-arm switching element is in the on state, the lower-arm switching element is in the off state. Considering PWM signals for turning on or off the switching elements, where the PWM signal supplied to the upper-arm switching element is PWM; the PWM signal supplied to the lower-arm switching element is /PWM that is an inversion signal.

Hereinafter, setting the upper-arm switching element to the on state is termed “upper arm on”, and setting the lower-arm switching element to the on state is termed “l(fā)ower arm on”.

Focusing on the above-described functions of the upper arm and lower arm, when viewed from the first step-up/step-down circuit CNV1, the arm (S1 arm) including the switching element S1 and the arm (S2 arm) including the switching element S2 are upper arms and the arm (S3 arm) including the switching element S3 and the arm (S4 arm) including the switching element S4 are lower arms. On the other hand, when viewed from the second step-up/step-down circuit CNV2 of the electric power converter 11, the S1 arm and the S4 arm are upper arms, and the S2 arm and the S3 arm are lower arms.