An image forming apparatus is disclosed having a fixing unit having a heating device, for heat fixing, a heating power supply section which is connected to the fixing unit to supply electric power supplied from a commercial power supply to the heating device, a voltage detecting section for detecting a value of voltage supplied to the heating power supply section from the commercial power supply, and a control section that stops a supply of electric power to the heating device from the heating power supply section if a first voltage value is smaller than a standard voltage value, while, compares a second voltage value detected by the voltage detecting section after the lapse of the standard time with the standard voltage value, and conducts control to stop operations for image forming if the second voltage value is smaller than the standard voltage value.