To provide a high-pressure space forming device which permits a human body to enter and exit very easily but has increased strength and closeness.

The high-pressure space forming device 1 includes a high-pressure vessel 10 capable of internally storing the human body, an opening 13 for entries and exits which is formed in the high-pressure vessel 10, a door 21 openably formed and opening or blocking the opening, and an opening reinforcing member 23 connecting the vicinities of the facing edges of the opening 13 and formed withdrawable to a withdrawal position at the time when the human body enters and exits.