An image forming apparatus includes a fixing device in which a width of a slide member is larger than a width of a pressurizing belt while both ends of the slide member are positioned outside of both ends of the pressurizing belt. The above-structured slide member makes it possible to prevent lubricant on the slide member from leaking out of the ends of the slide member and coming around the inner surface of the slide member, and thereby to prevent a pressing member beneath the slide member from swelling, resulting in avoidance of wrinkle generation on recording materials.