A fixing device includes a fixing belt, exercitation coils for induction-heating the fixing belt, power supplies that supply high-frequency power to the excitation coils, an output power detecting circuit that detects output electric energy of the power supplies, a power control circuit that controls the output electric energy of the power supplies, and temperature sensors that detect the temperature of a surface portion of the fixing belt. When electric energy applied to the excitation coils during the power fall reaches minimum power set in advance larger than 0 W, the power control circuit maintains the minimum power while the temperature detected by the temperature sensors is within a predetermined control temperature range and controls output power of the induction heating power supplies to shift from the minimum power to 0 W when the detected temperature deviates from the predetermined control temperature range.