PURPOSE: To prevent an occurrence of cracks at a circumferential edge of fine hole by a method wherein a cylinder integrally formed with the circumferential edge of the fine hole is projected substantially in a vertical direction in respect to a side wall surface.

CONSTITUTION: Fine holes 71, 71... formed in a secondary air pipe 7 inject secondary air above an inner flame to assist a combustion of mixture gas. 61, 61... are formed in a side wall of an inner barrel 6. The fine holes 61, 61... cause the air out of the inner barrel 6 to flow into a combustion chamber B as a secondary air and then cylinders 611, 611 are projected at the combustion chamber B. Due to this arrangement, a strength of an inner circumference of each of the fine holes 611, 611 is improved. So, even if a thermal stress is applied repeatedly from the gas burner 1 to the fine holes 61, no cracks are generated at the circumference of each of the fine holes.