IMAGE FORMING DEVICE

PROBLEM TO BE SOLVED: To provide an image forming device, which changes timing of start and conclusion of detection of temperature grade so as to detect a temperature grade without generating error. SOLUTION: A temperature grade detecting means 131 is provided in a CPU 105a, and passing time when the detected temperature from a temperature sensor 3 rises by the predetermined time is detected so as to detect a temperature grade of a heater 119. The temperature grade detecting means 131 is provided with a temperature discriminating means 140 and a detection timing changing means 150, and operated by the temperature discriminating means 140 at the time of starting the detection of temperature grade, and a temperature detected by the temperature sensor 3 is discriminated whether it exists within a predetermined range from a range switching temperature or not. The temperature grade detecting means 131 is operated by the detection timing changing means 150 in response to the signal from the temperature discriminating means 140, and changes timing of start and conclusion of detection of temperature grade.