To provide a gas burner which judges the kind of fuel gas and also is switched automatically into the specification suitable for the judged fuel gas.

This burner judges the supply gas from the difference of the electromotive force of a thermocouple 23 caused by the length of the flame of a burner 10, and in case that the supply gas is judged DME, this opens and keeps a solenoid opening and closing valve 22 and supplies gas from both sides of jets 14a and 14c thereby increasing the gas flow rate, and besides this maintains the OFF state of an electromagnetic solenoid 13, so the opening of a damper 11 becomes small, and this burns normally at an appropriate air- fuel ratio. In case that the fuel gas is judged LPG, this closes the electromagnetic opening and closing valve 22 and jets fuel gas only from a center jet 14a, so the gas flow rate decreases more than that in the case of DME, and this burns with the same input. Besides, this enlarges the opening of the damper 11 by turning on the electromagnetic solenoid 13, and the flow rate of sucked air becomes equal to that in the case of DME, and this burns normally at an appropriate air-fuel ratio.