A fixing device includes a pair of rotating members, a heater, a detector, a calculator, a pulse width modulation circuit, and a controller. In at least one embodiment, the pair of rotating members is configured to fix a toner image on a recording medium. The heater is configured to heat at least one of the pair of rotating members to a process temperature when driven with an alternating current. The detector is configured to detect the process temperature. The calculator is configured to calculate an amount of heat to adjust the process temperature to a reference temperature. The pulse width modulation circuit is configured to generate a drive signal having a pulse width modulation cycle divided into first and second off times and an on time inserted therebetween. The controller is configured to control operation of the heater according to the drive signal.