PURPOSE: To simplify the connection of the pipes in an oxygen-enriching apparatus, and solve the problem of alarm buzzer inherent in the conventional circuit, by replacing two vacuum switches which have been necessary in the conventional method, with single vacuum switch.

CONSTITUTION: The oxygen-enriching apparatus is composed of the oxygen-enriching module 1 having a selective oxygen-permeation membrane, the vacuum pump 2 sucking air through said module, and the vacuum switch 11 to detect the vacuum degree of the vacuum pump 2. When the vacuum degree is lower than the preset level during the operation, the contact of the alarming circuit is operated by the vacuum switch, and when the vacuum degree of the vacuum pump is not lower than the preset level, the contact of the vacuum pump protection circuit is operated by the vacuum switch 11 to inhibit starting of the vacuum pump 2. The defect of the conventional system comprising the temporal failure of the action of the alarm buzzer to generate alarm when the vacuum degree is lower than a preset level during the operation, can be eliminated by this process.