PURPOSE: To shorten a wait time and save electric power by switching and powering on three high, intermediate, and low heaters incorporated in a heat roller according to the wait period, a stand-by period, and a copy period.

CONSTITUTION: The heat roller 1 incorporates the high-power, intermediate-power, and low-power heaters 3H, 3M and 3L; the three heaters are switched on in the wait time t0-t1 to speed up the start, and only the heater 3L is turned on in the stand-by time t1-t2 to maintain the temperature for the preperations for the next copying operation in power saving mode. Copying operation is started at a point t2 to perform the temperature control only by the heater 3H and save electric power, and then completed at a point t3, and the next copying operation is held in readiness only by the heater 3L. Therefore, this is effective to the shortening of the wait time, saving of electric power, excellent fixation, high- efficiency fixation, reduction in the temperature rise in the machine, prevention against toner blocking in the machine, etc.