A gas laser oscillation device includes a discharge part, a blower part, and a laser gas path. The discharge part excites a laser gas medium and the blower part blows the laser gas. The laser gas path forms the circulation path of the laser gas between the discharge part and the blower part. The blower part includes an impeller section, a drive section, and an intermediate chamber disposed between the impeller section and the drive section. In the impeller section, a rotating blade to be rotated by a drive section via a rotating shaft is disposed. In the intermediate chamber, a main space and a gas damper space are partially partitioned by a gas shielding member.