PURPOSE: To make the whole device small-sized together with to prevent contamination of the optical parts by lubricating oil by constituting a blower of a turboblower while isolating a laser gas casing from the outside by an intermediate chamber.

CONSTITUTION: A turboblower 15 is used as a blower for forced-circulating laser gas to a laser discharge tube. The turboblower 15 consists of a turboblade 16 rotating in a laser gas circulating path and the motor parts 17 and 18 driving this turboblade 16, while the motor parts 17 and 18 are arranged in the atmosphere. Further, an intermediate chamber 22 isolated from laser gas and the atmosphere by labylinth seals 23 and 24 is provided between the turboblade 16 and the aforenamed motor parts 17 and 18. In this way, since the turboblade 16 of the blower is isolated from the motor parts 17 and 18 by the intermediate chamber 22, contamination of optical parts by an oil component of bearing oil of a driving motor can be prevented.