An image forming apparatus including: a fixing device including a heater and a temperature sensor, and a controller configured to execute: first heater control processing including: first processing of driving the heater with a predetermined energization ratio for a first time period independently of the detected temperature of the temperature sensor; second processing of stopping the driving of the heater for a second time period independently of the detected temperature of the temperature sensor; the second processing being executed when the first processing has ended, comparison processing of comparing a detected temperature of the temperature sensor with a reference temperature, which is executed when the second processing has ended; and first determination processing of determining whether to execute the first processing again based on the result of the comparison processing which has been executed when the second processing had ended.