An image forming apparatus prevents the occurrence of the combinations of output wave numbers which are ineffective to suppress flicker in a case where a set heater temperature is significantly reduced. If the set temperature is significantly reduced from 200° C. to 130° C., for example, so that the reduced temperature does not require current to be applied to a ceramic heater, which can occur at the time of starting reverse conveyance of the recording sheet in the double-faced printing mode, temperature control is temporarily suspended and the output wave number of power controlled by a controller is varied to 0 waves based on the previously set combinations of 12, 10, 4 and 0 waves, for example, if the output wave number is varied from 12.