A heating device includes: a heat generating unit generating heat in response to energization of an alternating-current power supply; a zero-crossing signal generating circuit generating a zero-crossing signal in synchronization with a zero-crossing time of the alternating-current power supply; an energization regulating unit regulating an energization period of the heat generating unit by the alternating-current power supply; a voltage change rate detecting unit detecting whether a rate of voltage change of the alternating-current power supply at the zero-crossing time is equal to or larger than an predetermined value; a switching unit switching on and off a connection between the alternating-current power supply and the heat generating unit; and an energization disabling unit disabling energization of the heat generating unit by controlling the switching unit when the rate of voltage change is equal to or larger than the predetermined value.