To provide an AC discharge gas laser oscillator that improves cooling efficiency in an electrode, and stabilizes discharge.

In the AC discharge gas laser oscillator 1, a pair of opposite metal electrodes 7 is provided in a laser container 3, a metal thin-film section 11 formed on the surface of a flat dielectric 9 is jointed to the opposing side of the metal electrode by wax, the periphery of the metal electrode and the periphery other than the surface of the discharge section of the flat dielectric plate are shut tightly for covering by an insulator 17, having a relative dielectric constant smaller than that of the flat dielectric, and cooling water can be circulated in the metal electrode.