To solve such a problem that current conduction control itself becomes complicated when it is performed by estimating the temperature of an end part outside a paper passing area by the relation of temperature and paper size because it must be changed according to the paper size in order to prevent the temperature rise of the end part outside the paper passing area from occurring.

This device is provided with plural temperature detection means arranged at different positions, a temperature difference calculation means calculating difference between temperature detected by the temperature detection means and a control means controlling a heat source based on the difference between the detected temperature.