An image forming apparatus according to the present invention includes a heating roller 2 fixed at a predetermined position, a pressurizing roller 3 press-fitted to the heating roller 2 by a pressurizing mechanism 4 to be movable, and a hardness change detecting mechanism 310 which becomes electrically conductive when the pressurizing roller 3 moves due to thermal expansion of the heating roller 2, and which detects a hardness change of the heating roller 2.