A CPU detects a temperature of a central part of a heating roller. If the detected temperature does not exceed 180.degree. C., the CPU drives a central coil or a side-end coil for 0.4 second in accordance with a temperature difference between the central part of the heating roller and a side-end part of the heating roller. Then, the CPU drives the side-end coil or central coil for 0.2 second. Thereafter, the CPU detects the temperature of the central part and repeats the driving control until the detected temperature reaches 180.degree. C.