To provide an auxiliary chamber type gas engine capable of reducing backflow of unburned gas from a main combustion chamber to an auxiliary chamber with a simple structure.

The auxiliary chamber type gas engine includes a piston 6 movably stored in a cylinder block, a cylinder head 3 cooperating with the piston 6 and the cylinder block to segment a main combustion chamber 10, an auxiliary chamber member 4 disposed in the auxiliary chamber type gas engine and including an auxiliary chamber 11 formed inside, and an ignition plug 5 for igniting fuel gas supplied to the auxiliary chamber 11. The auxiliary chamber member 4 includes: a main nozzle hole 9a formed therein penetrating from the auxiliary chamber 11 to the main combustion chamber 10; and a branched nozzle hole 9b branched from the main nozzle hole 9a and penetrating to the main combustion chamber 10.