Abstract: An image forming apparatus includes a fixing device to fix a developer image on an image bearing medium. The fixing device includes a first roller with a rubber layer coated on a shaft, the first roller being in contact with the developer image on the image bearing medium, and a second roller with a rubber layer having a smaller deformation than the first roller rubber layer coated on a shaft. The first and second rollers are rotatably pressed against each other to form a nip. The rubber layer thickness h.sub.1 of the first roller satisfies 0.512H<h.sub.1 <H, where H satisfies the following equation: ##EQU1## where R.sub.1 : first roller radius (mm)E.sub.1 : Young's modulus of the first roller shaft (Kg/mm.sup.2)t.sub.1 : thickness of the first roller shaft (mm)h.sub.1 : rubber layer thickness of the first roller (mm)R.sub.2 : second roller radius (mm)E.sub.2 : Young's modulus of the second roller shaft (Kg/mm.sup.2)t.sub.2 : thickness of the second roller shaft (mm)h.sub.