A temperature control method for a fixing device, which includes a heating unit that heats a recording material; a temperature detecting unit that detects a temperature of the heating unit; and a temperature controlling unit that determines an amount of power supplied based on a detected temperature of the temperature detecting unit, and controls the temperature of the heating unit by supplying the determined amount of power supplied, wherein temperature is sampled by the temperature detecting unit at a prescribed cycle, and the amount of power supplied is determined on the basis of this detection result, and when the duty cycle of the determined amount of power supplied is no more than 50%, a first period during which power is intermittently supplied to the heating unit, and a second period during which a power supply to the heating unit is not permitted are set within the prescribed cycle.