A discharge duty that is a duty at which a switch is conductive takes a value obtained by dividing a product of a crest value of a single-phase AC voltage and a square of a cosine value of a phase of the single-phase AC voltage by a both-end voltage across a capacitor. A sum of a product of a rectifying duty that is a duty at which a converter is conductive and a rectified voltage output from the converter and a product of the both-end voltage and the discharge duty varies in a period that is a half of the period of the single-phase AC voltage.