To provide a fixing device of a fixing roller fixing system which prevents separation of a pressure roller from a fixing roller that is easily caused with pressure lowering of press-contact force between the fixing roller and the pressure roller.

In the fixing device 1, the pressure roller 30 is energized to the rotating fixing roller 20, whereby the pressure roller is brought into press-contact with the fixing roller 20, and recording material 8 is made to pass through a nip 25 formed between the pressure roller and the fixing roller, whereby fixing operation to fix an unfixed image on the recording material 8 is performed. The fixing device 1 includes an axle-to-axle distance elongation regulating condition to prevent an axle-to-axle distance between a rotary shaft 37 of the pressure roller 30 and a rotary shaft 27 of the fixing roller 20 from getting longer than a fixed distance by regulating axle-to-axle distance elongation in which the axle-to-axle distance becomes longer when the recording material 8 passes through the nip 25.