To make noise in operation low and to make equipment compact and light weight and also to make it conveniently portable in an oxygen concentrator using a SPA method and used for an at-home oxygen therapy.

This oxygen concentrator uses, as an air pump 2 which is one of its functional components, the one which is of scroll type having pressurizing capacity of less than 2 kgf/cm2G, flow rate within a range of 10 L/min to 30 L/min at that time and capacity of exhausting up to -600 mmHg vacuum, and makes it have both functions of pressure supply and vacuum exhaust of air by switching the flow between an inlet and an outlet with a solenoid valve 4. As for an electric motor for driving the air pump 2, the DC brushless one is used, and an adsorber 5 is divided into plural beds and packed with alumina and a highly efficient adsorbent.