An image forming apparatus includes: a paper conveying portion for conveying a paper; an image forming portion for forming a visible toner image on the paper being conveyed, with a toner in accordance with input image information; and a fixing unit for fusing and fixing an unfixed toner image formed on the paper to the paper by using a heat roller and a pressing roller, and is constructed such that the pressing roller is composed of a metal core that forms a core shaft of the pressing roller and an elastic part that covers an outer periphery of the metal core, and a heat capacity at a center portion of the pressing roller with respect to a direction perpendicular to a paper's direction of conveyance is smaller than heat capacities at both ends of the pressing roller.