To realize a preheating function and a cooling function with simple constitution without necessitating a special heating device and a special cooling device by providing a heat transfer member taking heat away from toner and a sheet heated by a heating body and a heat insulting member insulating the heat between the heating body and the heat transfer member.

This device is provided with the heat insulating member 34 on an upstream side and the heat transfer member 36 on a downstream side in the moving direction of a heat-resistant belt 12, and the members 34 and 36 are brought into contact with the belt 12. The heat generated in the heating body 44 is transferred to the sheet 54 and the toner 52 coming in contact with the belt 12 and the toner 52 is melted and fixed on the sheet 54. The heat in the heating body 44 is transferred to a preheating member 40, and the sheet 54 and the toner 52 are preheated. Meanwhile, since the member 34 insulates the heat between the member 36 and the heating body 44, the member 36 is not heated. Therefore, the heated sheet 54 and the fixed toner 52 from which the heat is taken away by the member 36 are cooled, and easily peeled from the belt 12.