When an abnormality occurs in a first voltage sensor that detects a voltage of a power line on a high voltage side or a second voltage sensor that detects a voltage of a power line on a low voltage side, an estimated voltage of the power line on the high voltage side is calculated based on a detected current of a reactor that is detected by a current sensor that detects a current of the reactor as the detected current, and a step-up converter is controlled using the estimated voltage of the power line on the high voltage side.