To provide a heating system, a fixing device and an image forming device having this heating system, capable of controlling switching of the electric continuity or cutoff to a heating means from a commercial power source without causing a flicker phenomenon.

These devices have a constant current output circuit 2 capable of freely switching either of the electric continuity or the cutoff to a heater 1 from a commercial power source and an MPU 13 for controlling switching of the constant current output circuit 2 according to a detecting temperature of a thermistor 34 so that the constant current output circuit 2 is attained by switching switching time rising or trailing voltage with a prescribed time constant.