A transformer accepts an AC voltage from an AC power source, transforms the AC voltage, and supplies the transformed AC voltage to first rectifying circuits. Similarly, another transformer accepts an AC voltage from an AC power source, transforms the AC voltage, and supplies the transformed AC voltage to second rectifying circuits. The first rectifying circuits convert the accepted AC voltage into a positive DC voltage, and the second rectifying circuits convert the accepted AC voltage to a negative DC voltage. The positive DC voltage and the negative DC voltage then are superimposed and outputted to a secondary side of a transformer in the AC circuits. The AC voltage outputted from the transformers in the AC circuits and the DC voltage formed by superimposing the positive and negative DC voltages outputted from the first and second rectifying circuits are further superimposed, and supplied to each developing section.