A fixing device includes a heat rotational member that fixes a toner, a pressure rotational member that presses the heat rotational member, a magnetic-flux generation unit, a detector, and a fixing controller. The magnetic-flux generation unit includes a switch unit for switching of power supply to a resonant circuit. The resonant circuit includes a coil that generates a magnetic flux for causing the heat rotational member to generate heat by induction heating, and a capacitor. The detector detects power consumption of the magnetic-flux generation unit. The fixing controller recognizes the power consumption in response to an instruction of target power, sets a switching frequency of the switch unit in accordance with the target power, and causes the switch unit to stop the power supply if a difference between the set switching frequency and the adjusted switching frequency exceeds a predetermined change width.