To obtain a printer which is mounted with an on-demand fixing device using a low-capacity heater and drives all the rotational loads by a single motor, and in which the failure of an image forming system is eliminated, the failure being caused by decreasing rotational speed when starting up the heater of the fixing device in order to rapidly start up the heater.

A main motor is switched to rotate at low speed when starting up the heater, and rotate at processing speed when the temperature of the heater comes to the vicinity of the target temperature. Amount of electrification for a drum is varied between in low-speed rotation and in high-speed rotation. Control is performed so that high voltage is not applied at all when starting up the heater. Then, transfer ATVC control is performed when rotating at the processing speed, and the transfer cleaning control is performed when starting up the heater.

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