To provide a gas nozzle device for burner that has a simple structure and obtains excellent combustion from maximum thermal power to minimum thermal power without increasing costs.

A gas nozzle device for burner is provided with a first nozzle part 6 and a second nozzle part 7 provided in the first nozzle part 6. The first nozzle part 6 includes a nozzle hole 9 and a first gas port 10 opened at a downstream end of the nozzle hole 9. The second nozzle part 7 includes a body part 11 having an external diameter smaller than a hole diameter of the nozzle hole 9, a second gas passage hole 12 formed in the body part 11, and a second gas port 13 formed at a downstream end of the second gas passage hole and opened with a diameter smaller than the first gas port 10. The second gas port 13 is located at an upstream end of the nozzle hole 9, or downstream from the upstream end of the nozzle hole 9, and opened to an intake 5 of a mixing pipe 1 from a position corresponding to an interior of the nozzle hole 9 with a diameter corresponding to the supply amount of fuel gas at the time of minimum thermal power.