A laser oscillator which can keep distributions of pressure of a laser medium inside of a plurality of discharge tubes constant while making the laser medium circulate without stagnating. The laser oscillator is comprised of a first discharge tube, second discharge tube, first light guide, laser medium flow path, and blower. A flow resistance of a laser medium flow path between the blower and the first discharge tube and a flow resistance of the laser medium flow path between the blower and second discharge tube are the same as each other. A flow resistance of the laser medium flow path between the blower and a first end of the first light guide and a flow resistance of the laser medium flow path between the blower and a second end of the first light guide differ from each other.