A printer is provided that is capable of accurately detecting whether a recording medium is remaining even where a temperature changes rapidly. The printer has a fusing unit rotating to fuse a developer attached to a recording medium P onto the recording medium P with heat, a heater applying heat to the fusing unit, a temperature detection element detecting a temperature of the fusing unit heated by the heater, a timer measuring a time duration, a temperature gradient calculation unit calculating a temperature gradient of change in the temperature of the fusing unit based on a detection result of the temperature of the fusing unit detected by the temperature detection element, and a CPU determining whether the recording medium P is remaining on the fusing unit based on the temperature gradient calculated by the temperature gradient calculation unit and a time duration of the temperature gradient measured by the timer.