To provide a gas laser device for exposure which has no expansion of spectrum line width even if it is operated for a long time after a pause for a specified period of time.

The gas laser device for exposure comprises a laser chamber 1 and a band narrowing unit 4 for housing a band narrowing means for narrowing the band of light which is incident from the laser chamber 1. The band narrowing unit 4 holds a slit 5 so that an opening 54 may be positioned on an optical path between the band narrowing means and the laser chamber 1. The gas laser device is also provided with temperature increase suppressing means 51, 52 and 56 for suppressing the increase in temperature near the opening 54 of the slit 5.