Option fixing device

Disclosed is an option fixing device U 3 which is detachably coupled to an image forming apparatus U 1 of the type in which a toner image formed on a surface of a photosensitive member PR is transferred onto a recording sheet, the toner image is fixed onto the recording sheet by a fixing unit F′ contained in the image forming apparatus U 1 , and the recording sheet bearing the toner image fixed thereon is discharged through a sheet discharge port Ka. The option fixing device includes a sheet entrance port 2 a, a first sheet transport path SH6 which receives a recording sheet S coming through the sheet entrance port 2 a and discharges the recording sheet S without passing the recording sheet S through a fixing unit F, a second sheet transport path SH 7 which causes the recording sheet S to pass through the fixing unit F and then discharges the recording sheet S, and the fixing unit F for fusing and fixing a toner image on the recording sheet S being transported on and along the second sheet transport path SH 7.