PROBLEM TO BE SOLVED: To balance between improvement of a medical treatment effect and suppression of waste of an oxygen gas.SOLUTION: An oxygen supply device 10, for use in supplying a patient with an oxygen gas, includes: an oxygen output port 13 being an output port of the oxygen gas to outside of the device a respiration synchronism part for synchronizing ejection of the oxygen gas from the oxygen output port 13 with a respiration timing of the patient so as to allow ejection of the oxygen gas from the oxygen output port 13 intermittently: and a control part 15 for controlling ejection of the oxygen gas from the oxygen output port 13 continuously instead of synchronizing with the respiration timing of the patient on the basis of a measurement result of the oxygen saturation of the patient.
