A fixing device built in an electrophotographic image forming apparatus and a temperature control method for the fixing device are provided. The fixing device comprises a power supplying unit for supplying power to the fixing device; a control variable determination unit for determining control variables corresponding to operating states of the fixing device, wherein the control variables are used to control a temperature of the fixing device; a temperature detection unit for detecting the temperature of the fixing device; and a temperature control unit for controlling the temperature of the fixing device by using the control variables, wherein the temperature control unit comprises a duty ratio adjustment unit for adjusting a duty ratio of the supplied power based on the determined control variables. In addition, the control variable determination unit determines the control variables corresponding to at least one of a plurality of operating states.