PURPOSE: To make a simple structure of a gas burner and facilitate its manufacturing by a method wherein a desired number of fine holes are formed in a side wall of a combustion casing, a suction fan is operated to absorb and discharge the combustion gas at a gas burner out of the combustion casing.

CONSTITUTION: A gas burner 1 and a suction fan 9 are installed within a combustion casing 6. The desired number of fine holes 61 are formed in a side wall of the combustion casing 6 and a suction fan 9 is operated to cause combustion gas at a gas burner part 1 to be sucked and discharged out of a combustion casing 6. As the suction fan is operated, a part within the combustion casing becomes a negative pressure, a secondary air is supplied into the combustion casing through the fine holes. So, since it is not necessary to supply pressurized air by arranging the secondary air, its structure is simple and its manufacturing is easily performed.