To allow easy opening and closing of a lid for an opening of a sealing type pressure container using an O-ring.

The groove width of the O-ring of an opening is made slightly smaller than the thickness of the O-ring to be used. The groove depth is made slightly larger than the thickness of the O-ring to be used. A pressure medium is filled and collected in the bottom of the O-ring. When the container is sealed, the pressure medium is filled to increase pressure to push up the O-ring. When the container is not sealed, the pressure medium is collected to reduce pressure to pull down the O-ring, thereby preventing a load from being applied to the lid and enabling easy opening/closing of the lid.