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