An image forming apparatus having a fixing device 26 that includes a fixing roller 30, a center coil 33a for induction heating a substantially central part in the axial direction of the fixing roller 30, side coils 33b, 33c for induction-heating end parts in the axial direction of the fixing roller, induction heating power sources 60, 61, 70, 71 which supply a high-frequency pulse voltage to these coils, and a power control circuit 58a which variably controls output power of the induction heating power sources 60, 61, 70, 71 so that the output power increases or decreases stepwise on a predetermined cycle, and has a function of selectively setting maximum power supply and a function of selectively setting the output power variance cycle.