PURPOSE: To prevent jamming paper from burning even if an operator performs unreasonable, forcible operation, by heating a fixing device in preheating mode right after the power source if a copying machine is turned on, and heating it up to fixation temperature when no fault is found through self-diagnosis and jam detection right after a blower is powered up.

CONSTITUTION: When the power source of a copying machine is turned on, a microcomputer heats a fixing device in preheating mode and also perform self- diagnosis other than jam detection. As a result, when no fault is found, a blower for the suction device of a conveyor belt device is powered up and then jam detection is carried out at the circumference of the fixing device 0.5 second later. When it is judged through the jam detection that there is no fault, the fixing device is heated up to set temperature. If the occurrence of a jam is judged, the power source is turned off and jam display is performed. Even if an operator turns on the power source forcibly and repeatedly, the fixing device is never heated up above the upper limit temperature of the preheating mode and the jamming paper never burns.