The objective of the present invention is to provide a 2-cycle gas engine that has a suppressed occurrence of NOx (nitrogen oxides) by promoting the pre-mixing of a fuel gas and air. The present invention is provided with: a cylinder (2); a cylinder head (3); a piston (4) that demarcates a combustion chamber (c) between the cylinder head (3) and the peripheral wall (2a) of the cylinder (2); a fuel gas injection means (8) that injects a fuel gas (8a, 8b) to the combustion chamber (c); an ignition means (10) that ignites the fuel gas within the combustion chamber; a scavenging port (6) that supplies air to the combustion chamber (c) when the piston (4) is positioned in the vicinity of bottom dead center; a fuel gas injection timing control means (12) that is configured in a manner so as to cause the injection of fuel gas (8b) by means of the fuel gas injection means (8) when the piston (4) is in an up stroke and the piston (4) is positioned 10-100 DEG before top dead center, and furthermore to cause the injection of fuel gas (8a) by means of the fuel gas injection means (8) when the piston (4) is positioned in the vicinity of top dead center; and an ignition timing control means (12) that ignites the fuel gas within the combustion chamber (c) by means of the ignition means (10) when the piston (4) is positioned in the vicinity of top dead center.