PURPOSE: To improve folding performance of a bed, expandability of a mattress, accessibility of a patient, serviceability, controllability and such by installing a means, which restricts fluid shift to the first and the second directions by strengthening restriction of the fluid flow that flows one side of a valve seat and weakening the restriction of the flow that flows the other side of the valve seat. CONSTITUTION: A valve device includes a double action cartridge valve 344 installed inside a housing 346. In a condition that the outer member of a cartridge valve 344 is placed at a halfway and valve seats 360d and 370b are both not closed, air may flow from a high-pressure chamber 350 to a control chamber 356 through a passage 364, and further, flows to a low-pressure chamber 352. A valve member 369 is contacted to the valve seat 360d by shifting of an extended member 370 from a position, where the extended member is completely standing against a base-part member, to the above part of the extended member. A mattress cell, related to a valve device 342, shrinks to cause an internal pressure becomes conformable to that of the low-pressure chamber 352 because an air-flow opening 357 is opened.