Fuser unit and imaging forming apparatus having the same

A fuser unit for an image forming apparatus in which printing is performed selectively in either a monochrome printing mode or a color printing mode and the number of sheets conveyed per unit time in the monochrome printing mode is larger than the number of sheets conveyed per unit time in the color printing mode, comprising:

• a set of a heat roller and a pressure roller for sandwiching and conveying a printing sheet while heating the printing sheet by the heat roller;
• a peripheral surface contact member which is in contact with the peripheral surface of the heat roller;
• an external heater for heating the peripheral surface contact member by applying electric energy;
• a contact member temperature sensor for detecting a temperature of the peripheral surface contact member;
• and
• a temperature controller for controlling an upper limit temperature of the peripheral surface contact member in accordance with the number of printing sheets conveyed per unit time;
• wherein the upper limit temperature of the peripheral surface contact member in the monochrome printing mode is set to be higher than the upper limit temperature of the peripheral surface contact member in the color printing mode.