An image forming apparatus includes a fixing device, an image reading unit, and a control unit. The fixing device includes a heating elements arranged in a main scanning direction, a band-shaped thin film which slides on the surface of the heating element while in contact with the heating element, and a rotatable body configured to press against a surface of the thin film to cause the thin film to rotate. The fixing device heats the heating elements when an inspection sheet is passed through the fixing device, the inspection sheet having plural images formed by using a decolorable developer, each of the images having an image density that differs in a sub-scanning direction of the image forming apparatus. The image reading unit reads an image of the heated inspection sheet and the control unit determines an operative state of each heating element based on the read image.