An abnormality detection method for detecting an abnormality in an image forming apparatus which includes a heating belt looped around a heating roller and a fixing roller, comprising: a first temperature detection step of detecting a temperature of one widthwise end portion of the heating belt using a first thermistor; a second temperature detection step of detecting a temperature of the other widthwise end portion of the heating belt using a second thermistor; a temperature difference detection step of outputting a rotation pulse signal when a temperature difference between the temperature of the one end portion which is detected in the first temperature detection step and the temperature of the other end portion which is detected in the second temperature detection step is no greater than a predetermined value and outputting a low level signal when the temperature difference is greater than the predetermined value; a first high temperature detection step of outputting a high level signal when the temperature detected in the first temperature detection step is a temperature in a normal operation and outputting a low level signal when the temperature detected in the first temperature detection step is a temperature in an abnormal operation, a second high temperature detection step of outputting a high level signal when the temperature detected in the second temperature detection step is a temperature in a normal operation and outputting a low level signal when the temperature detected in the second temperature detection step is a temperature in an abnormal operation, and a heater signal output step of outputting via an AND circuit a heating signal for causing a heating source to heat the heating belt, wherein the heating signal output step includes: when the rotation pulse signal is output in the temperature difference detection step and the respective high level signals are output in the first high temperature detection step and the second high temperature detection step, outputting the rotation pulse signal to the AND circuit to cause the AND circuit to output the heater signal to the heat source, and when the low level signal is output in any of the temperature difference detection step, the first high temperature detection step, and the second high temperature detection step, outputting the low level signal to the AND circuit to cause the AND circuit to stop outputting the heater signal to the heat source. a first temperature detection step of detecting a temperature of one widthwise end portion of the heating belt using a first thermistor; a second temperature detection step of detecting a temperature of the other widthwise end portion of the heating belt using a second thermistor; a temperature difference detection step of outputting a rotation pulse signal when a temperature difference between the temperature of the one end portion which is detected in the first temperature detection step and the temperature of the other end portion which is detected in the second temperature detection step is no greater than a predetermined value and outputting a low level signal when the temperature difference is greater than the predetermined value; a first high temperature detection step of outputting a high level signal when the temperature detected in the first temperature detection step is a temperature in a normal operation and outputting a low level signal when the temperature detected in the first temperature detection step is a temperature in an abnormal operation, a second high temperature detection step of outputting a high level signal when the temperature detected in the second temperature detection step is a temperature in a normal operation and outputting a low level signal when the temperature detected in the second temperature detection step is a temperature in an abnormal operation, and a heater signal output step of outputting via an AND circuit a heating signal for causing a heating source to heat the heating belt, wherein the heating signal output step includes: when the rotation pulse signal is output in the temperature difference detection step and the respective high level signals are output in the first high temperature detection step and the second high temperature detection step, outputting the rotation pulse signal to the AND circuit to cause the AND circuit to output the heater signal to the heat source, and when the low level signal is output in any of the temperature difference detection step, the first high temperature detection step, and the second high temperature detection step, outputting the low level signal to the AND circuit to cause the AND circuit to stop outputting the heater signal to the heat source. when the rotation pulse signal is output in the temperature difference detection step and the respective high level signals are output in the first high temperature detection step and the second high temperature detection step, outputting the rotation pulse signal to the AND circuit to cause the AND circuit to output the heater signal to the heat source, and when the low level signal is output in any of the temperature difference detection step, the first high temperature detection step, and the second high temperature detection step, outputting the low level signal to the AND circuit to cause the AND circuit to stop outputting the heater signal to the heat source.