A fusing apparatus in an image forming apparatus that heats a fusing unit by applying an induced current is provided. The flicker characteristics of the fusing apparatus are improved by gradually increasing the amount of induced current applied to the fusing unit for a predetermined amount of time so that the amount of induced current applied to the fusing unit is prevented from severely varying. The fusing apparatus comprises a fusing unit which is resistance-heated or induction-heated by applying an induced current and fuses toner onto paper using the heat. The fusing apparatus further comprises a pulse width modulation (PWM) signal generation unit which generates a PWM signal in response to the ON signal so that the amount of induced current input to the fusing unit gradually increases to a reference current.