To provide a gas engine reforming natural gas into reformed fuel, improving heat efficiency, and ensuring ignition and combustion in an auxiliary chamber.

In the gas engine, an auxiliary chamber control valve 8 is arranged in a communication opening 27 communicating a main chamber 1 with the auxiliary chamber 2, and the natural gas is reformed into the reformed fuel of H2and CO by the fuel reforming device 15 arranged on an exhaust pipe 30. A reformed fuel valve 17 is provided in an intake manifold 16 of an intake pipe, and the reformed fuel is fed to the main chamber 1 in a suction stroke. A natural gas fuel valve 3 is arranged in the auxiliary chamber 2 and the natural gas is fed to the auxiliary chamber 2 from the suction stroke to a compression stroke. In a latter half of the compression stroke, the auxiliary chamber control valve 8 is opened, a mixture of air and the reformed fuel is blown into the auxiliary chamber 2 from the main chamber 1, and a glow plug 18 is provided in an upper part of the auxiliary chamber 2 igniting and burning the natural gas in the auxiliary chamber 2 for assisting ignition and combustion of the natural gas.

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