The oxygen supply device supplying a user with an oxygen gas for inhalation comprises: a first sensor unit acquiring information on percutaneous arterial oxygen saturation (SpO2) of the user, a second sensor unit acquiring information on respiratory frequency per minute (BPM), and a control unit. Under the condition where the SpO2 level acquired by the first sensor unit is equal to or larger than the predetermined first threshold and the BPM value acquired by second sensor unit is equal to or larger than the predetermined second threshold, the control unit regards the condition as a possible sign of CO2 narcosis that exhibits an increase in PaCO2 level, and thus judges the condition as an abnormal sign. Then the control unit executes controls such as stopping supply of the oxygen gas to the user, and the like.