To enhance the fixing quality of a fixing device to continuously fix sheets of a plurality of sizes, a carbon nanotube sheet 75, in which a plurality of carbon nanotubes are arranged such that the longitudinal directions thereof are oriented in the same direction, is provided on the surface of a heating roller 70 so that the carbon nanotube sheet ranges from the position a predetermined distance inside and the position a predetermined distance outside of the position through which each of the both edges of a sheet P2 with smaller width dimension than a sheet P1 of the largest width dimension to be fixed passes.