An oxygen concentrator includes an oxygen generation unit, an oxygen discharge unit, a respiration waveform sensor connected to at least one of a passage and a cannula, a respiration waveform storage unit that stores a respiration waveform detected by the sensor, a flow amount adjustment unit provided on the passage, and a control unit that controls the flow amount adjustment unit based on the respiration waveform detected. The passage connects the generation unit to the discharge unit. The cannula is attached to the discharge unit. The flow amount adjustment unit discharges the oxygen from the discharge unit, when the sensor does not detect the respiration waveform. The flow amount adjustment unit does not discharge the oxygen from the discharge unit for a predetermined time during an exhalation time, based on the respiration waveform detected by the respiration waveform sensor, when the sensor detects the respiration waveform.
