An image forming apparatus includes a power controller that starts an examination mode by an external operation. The examination mode detects a temperature-resistance property of a resistive heat generator. The power controller supplies power at a predetermined power duty cycle to the resistive heat generator. The power controller obtains the power supplied to the resistive heat generator and a change in a temperature of the resistive heat generator, that is detected by a temperature detector, while the power controller supplies the power at the predetermined power duty cycle to the resistive heat generator. The power controller calculates the temperature-resistance property of the resistive heat generator based on the power and the change in the temperature that are obtained. The power controller adjusts a power duty cycle at which the power is supplied to the resistive heat generator based on the temperature-resistance property.