PURPOSE: To facilitate starting on a condition that an intake air amount during starting is little with regard to a torch ignition gas engine with a supercharger to burn lean combustion gas.

CONSTITUTION: A fuel-air mixture feeding device A for starting use only being separately arranged is installed in a fuel-air mixture feed pipe at the inlet of the supercharger compressor 07 of an engine. The device A comprises a temperature sensor 35 installed in a starting air intake pipe system; a switching and starting fuel gas cutoff valve 26 for starting ←→ operation togetherwith data from a flow sensor 36 and a number of revolutions of engine detecting sensor 37; and a starting fuel control device 33 to control a starting fuel control valve 27 and a starting air throttle valve 30.