To provide a gas fuel supply device for internal combustion engines, which can hold the injection pressure of gas fuel constant from when an engine has been cooled to when the idling of the engine has completed and can control fuel injection.

In the gas fuel supply device for internal combustion engines, which supplies the gas fuel vaporized from liquid fuel in a fuel tank 2 to a fuel injection valve 4, a primary vaporizer 11, which intervenes in the middle of a fuel supply pipe 6 to vaporize the liquid fuel, a gas fuel pressure sensor 37 to detect the pressure of gas fuel on the side downstream of the vaporizer 11 and a an ECU (throttle opening control means) 35 to restrict the maximum opening of a throttle valve according to the data of the gas fuel pressure from the fuel pressure sensor 37 are provided.