FIXING DEVICE

PROBLEM TO BE SOLVED: To provide a fixing device capable of precisely detecting temp. regardlessly of the width size of a transfer material and fixing a toner image. SOLUTION: In this device, when transfer material Ps with the narrow width is allowed to pass through a fixing nip part, a heater 32 corresponding thereto is turned on, and when the transfer material PL with the wide width is allowed to pass the fixing nip, the heater 33 corresponding thereto is turned on. The temp. can be detected at the place close to a paper passing area although a thermistor 34 is arranged at the end part of a heating roller. Since the temp. can be precisely detected regardlessly of the size of the transfer material, the occurrence of the fixing defect due to the deficiency of heat quantity of or a hot offset due to the excessive heat quantity can be prevented.