A laser oscillator comprising an electric discharge excitation part having a discharge tube, and generates laser by excitation discharge of a laser gas flow through the inside of the discharge tube, an optical resonance part which has optical components attached to outsides of end walls of the discharge tube, and resonates laser generated in the discharge tube, and blower piping which connects an intake port and exhaust port of the discharge tube to form a circulation path of laser gas. The end walls of the discharge tube are provided with through holes which connect the inside of the discharge tube and the optical components, and blocking members are arranged in the through holes so as to block the flow of laser gas through the through holes toward the optical components.