A fixing device 6 according to the present invention has an endless-shaped heating belt 8, a first and a second roller 9 and 10 for stretching the heating belt 8, and a pressure roller 11 for nipping paper 2, together with the heating belt 8. The first roller 9 is supported so as to be rotatable by bearings 13 arranged at both ends of the first roller 9. The second roller 10 is supported so as to be rotatable by bearings 14 arranged at both ends of the second roller 10. The bearing 13 for supporting the first roller 9 is arranged more inward in an axial direction Z1 of the rollers than the bearing 14 for supporting the second roller 10.