A fixing device for fixing an unfixed toner image on a recording sheet by passing the recording sheet through a fixing nip and applying heat and pressure to the recording sheet, the fixing device comprising: a heater including a resistance heater part and a supporting member, the resistance heater part having a positive resistance-temperature characteristic in a temperature range above a predetermined level, and the supporting member being insulative and supporting the resistance heater part such that the resistance heater part applies heat to the recording sheet; a current detector detecting a current supplied to the resistance heater part; and an abnormality determiner determining whether the resistance heater part has an abnormality, based on an initial current detected by the current detector at a predetermined time after a beginning of power supply to the resistance heater part and before the temperature of the resistance heater part reaches the predetermined level.