PURPOSE: To lessen the wear of a seal by executing the final movement of a door for closure perpendicularly to the surface of an aperture.

CONSTITUTION: When a piston 18, consequently a sleeve 19, are moved upward, the sleeve 19 lifts a door bracket 20 and the door 11 is moved upward. The sleeve 19 is installed rotatably on the bracket 20 in order to make the door 11 and a guide rod 14 movable in a horizontal direction. Two O-rings 21, 22 for sealing consisting of an elastic material are disposed on the wall 8 in order to ensure the good sealing between the door 11 and a wall 8. The entire part of the door 11 is attracted toward the O-rings 21, 22 for sealing by a vacuum suction effect, by which the good seal is obtd. The bracket 15 internally has a long hole to allow the passage of the guide rod and further a bolt 24 penetrating the hole and penetrating the guide rod is disposed in the bracket 25, by which the guide rod 14 is made movable in the horizontal direction.