To provide a heating device or the like capable of surely reducing a flicker as compared with a conventional one.

A D.C. controller circuit applies a zero-cross detection interrupt to a CPU when an on-signal from a zero-cross circuit is changed over to an off-signal, and the CPU 71 counts up the number of interrupts in each zero-cross detection interrupt. When the value of a counter for counting it is one, a /ON signal is turned on; when it is two, the /ON signal is turned off; when it is three, the /ON signal is kept turned-off and the counter is reset. The number of turning-on is further counted; and the /ON signal is continuously turned on even if the zero-cross interrupt is generated from the number of turning-on is four or more. As a result, the turning on/off of the /ON signal is repeated three times at timing shown in the figure, and the root-mean-square value of the current of a fixing heater 42 is set to a value shown in the figure. Thus the /ON signal can surely be set in the on-state or the off-state at the zero cross of the voltage value of commercial power as compared with a conventional one.