To prevent local temperature rise to improve the durability and safety of a heat roll in a heater where a partial area in the peripheral direction of the heat roll which quickly rises and can be rotated at a high speed is heated from the inside of the roll.

The fixing device 12 has a fixing roll 28 and a pressure roll 30 to be pressed to the roll 28, and a heat source 32 which heats the partial area in the peripheral direction of the fixing roll 29 is provided on the inside of the fixing roll 28. The temperature of the fixing roll 28 is detected by a thermistor 34. The fixing roll 28 is rotated during warming-up of the fixing roll till arrival at a preliminarily set temperature.