To provide a door mechanism for an air chamber apparatus, which considerably facilitates access to a pressurized container used for an air chamber, is opened and closed by a user by himself without requiring door opening closing operation by a third person when used, fully secures air tightness when the door is closed, and has an inexpensive cost and high performance.

A rectangular opening portion 2 is provided in the front top surface of a chamber upper part 29 of the pressurized container which a user enters. A rectangular door having a curved surface having substantially the same shape as the peripheral surface of the chamber is disposed on the inside of the opening portion 2. The door has a size slightly larger than the opening portion 2, the peripheral edge of the door overlaps an inner wall surface of the chamber, and the air tightness is formed between the door and the inner wall surface of the chamber upper part 29. Rails are provided at the edges of the door and on the inside of the edges of the opening portion 2, respectively, and the door is moved to the back side of the chamber upper part 29, parallel with the wall surface of the chamber upper part 29, and is allowed to be opened and closed.