PURPOSE: To make discharge start voltage lower than discharge holding voltage by newly providing a trigger electrode for discharge starting.

CONSTITUTION: The device has a flat plate from anode 1 and a plurality of bar form cathodes 4 which are studded upright so as to array in one direction in opposition thereto and is so constituted that a laser medium is supplied between these cathode row and the anode from the lateral direction and d.c. voltage 6 is applied between the anode and cathodes to generate glow discharge thereby inducing laser, wherein the provision of a trigger electrode 8 for discharge starting installed in parallel with the cathode row enables the discharge start voltage to be made lower than discharge holding voltage