To provide a fixing device capable of correctly and quickly grasp discontinuity of respective heaters with a simple constitution, and continuously performing the excellent fixing operation regardless of discontinuity on one side of a heater, with respect to the fixing device heating a fixing roller by two unit of heaters.

With regard to a first heating state that the heater 3 and the heater 4 are simultaneously turned on, the second heating state that only the heater 3 is turned on, and the third heating state that only the heater 4 is turned on, the first temp. rising value, the second temp. rising value and the third temp. rising value with respect to the reference time of the fixing roller 2, are respectively detected by a thermistor 5 and previously stored in a CPU 8. Then, in the case the temp. of the fixing roller 2 is below the temp. permissible of copying, the temp. up measuring value corresponding to the reference time of the fixing roller 2 detected by the thermistor 5 is, arithmetically processed based on the second temp. up value and the third temp. up value, and the abnormal discontinuity on the wire of either the heater 3 or the heater 4, is decided, therefore an operator is made possible to quickly and correctly recognize the discontinuity of either heater, and to appropriately facilitate a counter measure to the fixing operation.