A recording medium having a toner image formed thereon is moved to pass through a press contact portion between an endless belt being heated and an pressure roller pressed against the endless belt. When passing through the press contact portion, the toner image is fused and permanently affixed onto the recording medium. An oil application width O of an oil application roller is shorter than belt width B of the endless belt, and a maximum passing width P of a recording medium that may be supplied for the image formation, but is longer than a maximum image-forming width I within which an image may be formed on the recording medium.