To provide an air mattress, which is made inexpensive, lightened in weight, reduced in volume at the time of storage as well and easily handled, concerning the air mattress suitable for preventing bedsores.

This air mattress has double chamber structure composed of an airtight chamber 5 formed from the composite film of synthetic resin improved in gas barrier property and reduced in extension and a pressure regulating chamber 6 formed from a film having fine air holes over all the surface while incorporating a foaming member 8. Then, when a person lies on his back or on his stomach on the air mattress, the foaming member 8 is crushed by discharging gas contained in the foamed member 8 inside the pressure regulating chamber 6 from the fine air holes arranged over all the surface of film concerning pressure from the upside of whole body and pressure corresponding to a projecting part such as the waist partially strongly pressed, flatness on the upper surface of body is kept by lowering pressure in the airtight chamber 5 and loosely sinking such a section and when the load is partially changed by tossing about during sleeping, the gas inside the pressure regulating chamber 6 is made adaptive corresponding to that change by compressing the foamed member 8, restoring it and repeatedly discharging/sucking gas from the fine air holes over all the surface of film.