Abstract: Disclosed is an oxygen generator with improved noise and vibration reduction, compactness, and user convenience. The oxygen generator includes a gas separation membrane module including: gas separation membranes formed of a bundle of hollow fiber membranes; an atmospheric air inlet, to one end of which one end of the gas separation membranes is bonded, sealed, and attached, and the other end of which air in the atmosphere enters; a nitrogen outlet, to one end of which the other end of the gas separation membranes is bonded, sealed, and attached, and the other end of which nitrogen exits; a guide rail where the gas separation membranes are wound in a coil and stored on an inner surface thereof; a gas separation membrane module casing containing the guide rail where the gas separation membranes are stored.