Abstract: A door is mounted within a doorway to be pivotal about a pivot axis disposed close to and along one of side surfaces of the doorway to selectively open and close the doorway. A guide roller protrudes toward the upper surface of the doorway from the upper edge of the door at a location remote from the location of the pivot axis when the door is closed. A guide rail extends along the length of the upper surface of the doorway for guiding the guide roller along the length of the upper surface of the doorway. The guide rail is pivotal about the pivot axis. Means is provided to disengageably engage the guide rail with the upper surface of the doorway.