A fixing device for fixing an image formed on a sheet member is disposed on a transportation path for transporting the sheet member thereon. The fixing device can be attached to or detached from the main body of an image forming apparatus, and a guide member is provided in the image forming apparatus for guiding the fixing device when it is attached to or detached from the main body of the image forming apparatus. The guide member includes an inclined surface on which the fixing device is placed to be guided upward for attachment. If the fixing device is unlocked from the main body of the image forming apparatus at the time of maintenance or the like, the fixing device is moved outwardly along the inclined surface due to its own weight.