To provide an image forming apparatus capable of improving fixing of images to paper while preventing occurrence of curl and wrinkle on the paper when the image forming apparatus or a press roller is cold and the large paper having the size larger than the prescribed size is to be fixed.

The image forming apparatus judges whether the press roller 72 (image forming apparatus 10) is cold or not based on a temperature inclination of a heat roller 68, and instantaneously increases a fixing temperature of the heat roller 68 to maintain the high temperature during only a prescribed time period (ts in fig.2) when the press roller 72 (image forming apparatus 10) is cold and paper size is B4 size or more.