An oxygen concentration of a pressure swing adsorption type which prevents theexcessive adsorption of oxygen molecules accompanying the excessive supplyof raw-material air and prevents the decrease in product oxygen concentrationaccompanying argon enrichment, the excessive adsorption and the decrease occurringwhen the oxygen supply rate is set at a value in a low-rate range. It reduces powerconsumption and realizes the stable operation of a compressor. The concentratorcomprises: at least one adsorption bed packed with an adsorbent capable of moreselectively adsorbing nitrogen than oxygen an air supply means for supplyingpressurized air to the adsorption bed a channel switching means for repeatingat a given timing an adsorption step in which the air sent from the air supply meansis supplied to the adsorption bed to take out concentrated oxygen and a desorptionstep in which the adsorption bed is evacuated to regenerate the adsorbent anda flow rate setting means in which the rate at which the concentrated oxygen issupplied to a user is set. The oxygen concentrator is characterized in that thechannel between the air supply means and the adsorption bed is equipped with adischarge piping having a discharge valve for discharging part of the pressurizedair to be supplied to the adsorption bed into the air.
