A high-voltage power supply to output a plus/minus high-voltage, which is applied to image forming apparatuses, includes a plus high-voltage output unit outputting the plus high-voltage by using a Pulse Width Modulation (PWM) signal, a minus high-voltage operation control unit charging a certain voltage while the plus high-voltage output unit is outputting the plus high-voltage, a minus high-voltage output unit outputting the minus high-voltage by using the certain voltage charged in the minus high-voltage operation control unit, and a minus high-voltage blocking unit to block the output of the minus high-voltage from the minus high-voltage output unit while the plus high-voltage output unit is outputting the plus high-voltage.