A fixing member having an outer peripheral surface brought in pressure contact with a sheet, an induction coil along the member, and a high frequency power source section that heats the heat generating layer of the fixing member by supplying an alternating current to the induction coil. A magnetic flux regulating section that restricts the generation of heat in a specified region of the fixing member in the widthwise direction of the sheet is provided. Image regions occupied by the image to be fixed are detected in the widthwise direction of the sheet. Control of specifying the region in which the generation of heat should be restricted for the magnetic flux regulating section is executed so that only regions corresponding to the image regions of the fixing member are substantially heated in the widthwise direction of the sheet, sheet-by-sheet according to the result of detection.