A respiratory information acquisition device used for a PSA type oxygen concentration device that switches and uses multiple adsorption cylinders includes a respiratory information acquisition means of measuring a first pressure of a periodic pressure fluctuation in an oxygen supply path when oxygen is supplied to a patient from the PSA type oxygen concentration device and a second pressure of a periodic pressure fluctuation in the oxygen supply path when oxygen is not supplied to the patient from the PSA type oxygen concentration device, a phase confirmation means of matching phases of the first pressure and the second pressure, and a subtraction processing means of calculating a difference between the first pressure and the second pressure in the condition where the phases are matched.