A fixing apparatus of an image forming apparatus of the present invention, in arrival timing of a temperature falling area of a heat roller passing a nip at opposite position .gamma. of an induction heating coil from temperature detection position .beta. by an infrared temperature sensor around the heat roller, according to detection results by the infrared temperature sensor, controls an output value of the induction heating coil under control of an inverter circuit, heats and returns the heat roller in real time to a fixable temperature, and realizes energy conversation. At the time of arrival at the nip, the heat controller is always set to a fixed fixable temperature, thus in a fixed image, a high image quality free of ripple marks can be obtained.