PURPOSE: To prevent the freezing of a part close to a hot water passage of a main regulator in any circumstance in the hot water passage to thermally insulate the regulator to decompress the high pressure fuel gas to feed it to the gas engine.

CONSTITUTION: The hot water of high temperature used in cooling a gas engine flows in a hot water passage 13 inside a main regulator 11 to decompress the high pressure fuel gas and feed the majority of the amount of the required fuel by the gas engine and a hot water passage inside a sub regulator 12 to feed the rest of the required fuel to the gas engine to thermally insulate the main regulator 11 and the sub regulator 12. The hot water passage inside the main regulator 11 and the hot water passage inside the sub regulator are connected in series 13 to each other to allow the hot water of high temperature to flow from the main regulator as the hot water passage structure of the regulator of the gas engine 1 where the hot water of low temperature after finishing the thermal insulation is returned to the gas engine.