The present invention provides an image fixing device for fixing toner on a transfer member comprises a heat roller which is a hollow cylindrical member rotatably supported at both end portions and having heating means inside thereof, pressure means press-contacted to the heat roller for pressing the transfer member passing between the heat roller and the pressure means against to a peripheral surface of the heat roller, and the pressure means is a pressure roller disposed approximately parallel to the heat roller and supported rotatably, at least one of the heat roller and the pressure roller has a layer of elastic material on its peripheral surface, and a value A/B is set to be within a range from 0.7 to 0.8 wherein A represents a nip width at an approximate central portion of an area between the heat roller and the pressure roller where the transfer member passes through and B represents a nip width at end portions of the area.