Patent ID: 7693472

Claim:
An image forming apparatus comprising: a recording medium conveying portion for conveying a recording medium; an image forming portion for forming a visible developer image on the recording medium being conveyed, with a developer in accordance with input image information; and, a fixing portion for fusing and fixing the visible developer image formed on the recording medium to the recording medium by using a heat roller and a pressing roller, the heat roller having an internal heater extending across a full width of the heat roller, wherein, 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 is constructed so that a heat capacity at a center portion of the pressing roller with respect to a direction perpendicular to the recording medium's direction of conveyance is smaller than heat capacities at both ends of the pressing roller, wherein as the heat roller is heated in its full width by the internally provided heater the temperature at outermost edges of a recording medium passage area of the heat roller becomes higher as compared to a temperature at a central portion thereof due to a recording medium having a width less than the width of the recording medium passage area being conveyed between the heat roller and the pressing roller, wherein the ends of the pressing roller extend at least to outermost edges of a recording medium passage area such that a heat capacity of the pressing roller at an outermost edge of the end is a maximum as the recording medium is being conveyed.