PURPOSE: To allow easy switching of the fuel and to enable shifting from high fire to low fire while complete combustion is maintained, by a method wherein a 2-system flow passage part, through which gas and petroleum pass, is installed in a burner body, and a control valve for controlling an amount of the air to be fed in the flow passage part is mounted.

CONSTITUTION: In the case of fuel oil, a burner ignition is conducted such that a pilot 65 is ignited, and a fuel valve 59 is gradually opened by a control motor 43. In which case, an air intake 25, simultaneously, is controlled. In the case of gas, through backward movement (in the direction of an arrow mark (b)) of a rod 53 to its fullest size, a communicating port 31 for primary air is fully closed by a control valve 57. The pilot 65 is ignited and a gas control valve 23 is gradually opened to perform ignition of a burner, and simultaneously, an air intake amount is controlled by the control motor 43. In this case, regulation of a blade 49 and a piston blade 50 causes formation of a flame into a proper shape. Through forward movement (in the direction of an arrow mark (a)) of the rod 53, the communicating port is gradually opened to feed a primary air in the flow passage part 9, and this permits the flame to be controlled into a flame in a complete combustion state.