PURPOSE: To provide an image forming device capable of being stably kept at a prescribed temperature while an image is formed by only one conventional, inexpensive and simple temperature control circuit by controlling the temperature by selecting a heat source when the number of image forming sheets are only one and when two or more.

CONSTITUTION: This device is provided with a fixing roller part 1 thermally fixing toner, the first heat source 2 executing a heating action at high electric power in the roller part 1, the second heat source 3 executing the heating action at the lower electric power than the first heat source 2, a temperature control part 4 setting the temperature to a designated value, a heat source selection part 5 selecting one heat source and a number-of-sheet judgement part 6 judging a first state when the number of image forming sheets are only one or a second state when two or more. In the case of the first state by the judgement part 6, the second heat source 3 is selected. In the case of the second state, the first heat source 2 is selected.