PURPOSE: To obtain an exact temperature control characteristic by a simple adjusting operation by generating a reference signal referring to control data suited to a preliminarily measured, temperature detection characteristic inherent in the fixing device, or correcting a temperature detection signal.

CONSTITUTION: A control device 15 sets control data suited to a preliminarily measured and indicated, temperature detecting characteristic inherent in the fixing device 13 in a control data storage means, generates a reference signal, or corrects a temperature detection signal referring to the control data, when the temperature of a heating roller 13a is controlled. As a result, the reference signal or temperature detection signal which becomes an object of comparison for the purpose of temperature control, can be suited to the temperature detecting characteristic inherent in the fixing device. Thus, an exact temperature control characteristic can be obtained by simple operation.