A fixing device of the present invention has a fixing belt that is brought in contact with a recording medium to heat and fix a developer image formed on the recording medium. Plural supporting rollers support the fixing belt rotatably. Pressing rollers are provided opposing to the supporting rollers via the fixing belt for clamping and conveying the recording medium jointly with the fixing belt. A temperature controller raises the temperature of a heating roller to a second set temperature from a first set temperature after the temperature of the fixing belt drops to a prescribed temperature lower than that in the heating and fixing state, when shifting to the ready state after the heating and fixing state is complete.

An electrophotographic image forming apparatus and method of controlling the apparatus during a warm-up operation. During the warm-up operation, a heating unit for heating a fuser will be turned on and a motor for starting rotation of a photosensitive body will be activated when the temperature of the fuser reaches a motor rotation start temperature. When the temperature of the fuser reaches a warm-up completion temperature, the warm-up operation will be stopped and the rotation of the photosensitive body will be terminated. The warm-up completion temperature is higher than a stand-by temperature but lower than a fusing temperature.

An image-forming device in which an image is formed on a transfer material by superposing the transfer material with a photosensitive material on a heating drum. By altering a duty ratio of a control signal from a controller to a heater driver, a heater is controlled such that surface temperature of the heating drum is fixed. At times other than during image-formation, during which precise control is required, the period of the control signal (i.e., of on/off control of the heater) is lengthened. Thus, "flicker" can be suppressed.