An image forming apparatus is provided with: a heating unit which generates heat to fuse a toner on a printing medium; a switch which selectively supplies alternating current (AC) power to the heating unit; a first switching driver which drives the switch to supply the AC power to the heating unit; and a first supply limiter which allows the AC power to be supplied to the heating unit by the first switching driver if a polarity of the AC power is the same as a preset polarity, and cuts off the AC power supplied to the heating unit if the polarity of the AC power is opposite to the preset polarity.