To provide a gas engine device capable of providing excellent ignition property and high heat efficiency, reducing exhaust amount of nitrogen oxide, and preventing knocking.

In this gas engine device for supplying gas fuel and oxidizer into a combustion chamber formed by a cylinder 1 and a piston 4 to ignite air-fuel mixture compressed in the combustion chamber by an ignition device 5, the ignition device 5 generates plasma having ultra-high temperature by detonation of fuel and has an injection preliminary chamber 16 extending in the direction in which plasma progresses and a plurality of injection holes 17 extending radially from the injection preliminary chamber to form an injection opening 17B in an outer peripheral part. Each injection opening forms a thin and long slit shape in the direction of the axis of the cylinder.