To avoid the interference of the opening/closing of a door against a person and a case and, further, clean the inside surface of the door easily by a method wherein a door reciprocal movement mechanism by which a shaft supporting part which supports the one end side of the door is reciprocally moved along the opening of a vacuum chamber is provided.

When a door 20 is closed by a door opening/closing mechanism 30, after an attaching block 32 is transferred to an upper end by a vertical driving mechanism 31, a clamping mechanism 50 is made to operate and clamping rollers 22a and 22b are transferred to press a door main part 21 against a sealing surface 16. When a work is put into/taken out of the chamber main part 11 of a vacuum chamber 10, and the chamber main part is cleaned, the attaching block 32 is transferred to a lower end by the vertical driving mechanism 31. Further, the door 20 can be tilted toward this side with a pin 23a as a rotary shaft. With this constitution, the door can be opened/closed without the interference against workers, etc., in front of the door. Further, the door can be tilted, so that the inner wall surface of the door can be cleaned easily.