A fuser unit including: 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.