An image forming apparatus comprising an induction heating circuit for a fixing device of an image forming apparatus, the induction heating circuit comprising: an electrically conductive heating element for generating heat using an induction heating method; an induction coil configured to generate a magnetic field for induction heating; temperature detection means configured to detect a temperature of the electrically conductive heating element; driving signal generation means (20, 112) configured to determine a frequency of a driving signal which becomes equal to or higher than a set minimum frequency for driving the induction coil, according to a difference between a temperature detected by the temperature detection means and a target temperature (To) of the electrically conductive heating element, and to generate the driving signal, the electric power supplied to the induction coil being increased as the frequency of the driving signal is closer to the minimum frequency; current detection means configured to detect a current corresponding to electric power supplied to the induction coil; and characterized in that further comprising; control means configured to, if the frequency of the driving signal is the set minimum frequency and the detected current is less than the current value detected by the current detection means when the frequency of the driving signal becomes the set minimum frequency under a condition that electric power is supplied to the induction coil during normal operation, generate a signal representing an abnormality in the supplied electric power, to stop formation of a toner image onto a sheet when the signal representing the abnormality is generated, wherein the minimum frequency is set at a frequency slightly higher than a resonant frequency of the induction coil. an electrically conductive heating element for generating heat using an induction heating method; an induction coil configured to generate a magnetic field for induction heating; temperature detection means configured to detect a temperature of the electrically conductive heating element; driving signal generation means (20, 112) configured to determine a frequency of a driving signal which becomes equal to or higher than a set minimum frequency for driving the induction coil, according to a difference between a temperature detected by the temperature detection means and a target temperature (To) of the electrically conductive heating element, and to generate the driving signal, the electric power supplied to the induction coil being increased as the frequency of the driving signal is closer to the minimum frequency; current detection means configured to detect a current corresponding to electric power supplied to the induction coil; and characterized in that further comprising; control means configured to, if the frequency of the driving signal is the set minimum frequency and the detected current is less than the current value detected by the current detection means when the frequency of the driving signal becomes the set minimum frequency under a condition that electric power is supplied to the induction coil during normal operation, generate a signal representing an abnormality in the supplied electric power, to stop formation of a toner image onto a sheet when the signal representing the abnormality is generated, wherein the minimum frequency is set at a frequency slightly higher than a resonant frequency of the induction coil.