To provide an image forming device capable of optimally detecting a fault by setting detection time or/and detection temperature for deciding the fault to an optional value based on room temperature information by a room temperature detecting means.

This image forming device is provided with a heating temperature detecting means 515 detecting the temperature of an image heating device 510 in order to control the temperature of the device 510, the room temperature detecting means 106 detecting the room temperature, and a fault detecting means 13a deciding the fault of the device 510 according to the temperature detected by the detecting means 515. The detecting means 13a sets the detection time for deciding the fault to the optional value based on the room temperature information by the detecting means 106.