An oxygen concentration apparatus (300) according tothe present invention has: pressure swing adsorption typeoxygen concentration means (310)； and a control means(350) that controls switching means (316) that switchesbetween intake of pressurized air into an adsorptioncolumn (312) and exhaust from the adsorption column. Theswitching means is controlled based on pressure in oxygenconcentrated gas in the conduit measured by pressuremeasuring means to adjust a cycle of adsorption andregeneration processes of the oxygen concentration meansso that pressure at the upstream of flow rate adjustingmeans (340) can be controlled and, as a result, the needfor a mechanical pressure regulating valve, that has beenneeded conventionally, can be eliminated. Further, thereis also shown a gas supply apparatus that comprisesultrasonic type gas concentration and flow rate measuringmeans that comprises, in turn, two ultrasonic transducersthat is disposed in an opposed manner in the conduitthrough which product gas flows so that a concentrationvalue measured when the product gas output is stopped isdetermined to be a product gas concentration.
