To input saved electric power in a heating system of a magnetic induction heating method.

ON width control of a switching element 271a of an inverter circuit 271 of a voltage resonance method and ON-OFF control are simultaneously used as a control mode of a power source (an exciting circuit) 27 for supplying electric power to a magnetism generating means (an exciting coil) 18. That is, in an ordinary state, the electric power is controlled under ON width control of the switching element 271a of the inverter circuit 271, and when controlling the electric power not more than a minimum ON width, an ON width of the switching element 271a is fixed to the minimum ON width, and the electric power is controlled up to large electric power from small electric power by repeatedly controlling ON-OFF. Thus, even if the magnetic induction heating method is adopted as the heating system of an image forming device, a continuous print is satisfactorily performed.