A vacuum container (10) of a laser oscillator (30), said vacuum container (10) comprising: a tube (11) having a cylindrical shape or a polygonal cylindrical shape; an insertion member (12) into which said tube is inserted; anda first seal member (15) and a second seal member (16) disposed between the tube and the insert member, the first seal member being made of a material whose corrosion resistance is higher than that of the second seal member, the first seal member with respect to second seal member is disposed on a vacuum side, the second seal member is made of a material whose sealing property is higher than that of the first seal member, and the first seal member at least partially comprises a deformation portion (18a to 18e) which deforms so as to improve its sealing property wherein the deformation portion (18a) is deformed due to a reduction in pressure around the first seal member.
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