To maintain combustion performance such as flame holding performance and suitably prevent backing of flame etc.

In a burner port formation part 8 of a burner head 3, a radially formed burner port 9 is formed by a pair of inner burner ports 10, 10 opened at an upstream end of air fuel mixture and an outer burner port 11 with which the inner burner ports 10, 10 are merged and which is opened at a downstream end of air fuel mixture and having width wider than the single inner burner port 10.