When the temperature of a fixing roller detected by a temperature detecting section is less than a predetermined fixing temperature, and a determining portion determines that an image forming unit forms a color image, a control portion stops electric power supply from an electric double layer capacitor to a second fixing heater and allows a commercial power source to supply electric power to a first fixing heater to heat the fixing roller. When the determining portion determines that the image forming unit forms a monochromatic image, the control portion allows the commercial power source to supply electric power to the first fixing heater to heat the fixing roller and allows the electric double layer capacitor to supply electric power to the second fixing heater to heat the fixing roller.