To provide a heating device capable of switching resistance values, detecting a failure state in the heating device with a simple configuration and improving reliability of itself.

The heating device comprises: a voltage detection section 207 to detect whether power supplied to a heater 300 is in a state of overpower by detecting a half wave of a positive phase of an AC waveform of commercial AC power supply 201 applied to a conductive path H2 of the heater 300; an voltage detection section 208 to detect whether power supplied to the heater 300 is in the state of the overpower by detecting a half wave of a negative phase of the commercial AC power supply 201 applied to the conductive path H2 of the heater 300; and a relay control section 204 to stop power supply from the commercial AC power supply 201 to the heater 300 if overpower is detected by either the voltage detection section 207 or the voltage detection section 208.