One partial reflecting mirror (19) and two total reflecting mirrors (21
and 23) being placed at one end of a resonator (12) and three
total reflecting mirrors (20, 22, and 24) being placed at an opposite
end of the resonator (12) are included, and the reflecting mirrors (19,
21, and 23 and 20, 22, and 24) are placed so that the
centers of laser light on the three reflecting mirrors (19, 21, and 23;
20, 22, and 24) placed at each end of the resonator forms a triangle.
Two (19 and 21; 20 and 22) of the three reflecting mirrors
(19, 21, and 23; 20, 22, and 24) placed at each end of the
resonator (12) are placed at a downstream end of a discharge area in a direction
in which a laser medium (10) flows.
