To suppress generation of NOx and unburnt components while reducing the resistance in a duct and the manufacturing cost by forming a concave combusting part of knit-like heat resistant metallic fibers at the forward end of a premixed gas supply pipe.

The burner 1 generating hot air has a concave combusting part 4 formed of knit-like heat resistant metallic fibers 3 at the forward end of a premixed gas supply pipe 2. The knit-like heat resistant metallic fibers 3 are produced by knitting or weaving metallic fibers. It is commercially available as a metal fiber knit, for example. Although a conical combusting part 4 is shown, various profiles can be employed. The combusting part 4 is obtained by forming a mesh support 5 of specified shape from an expand metal, or the like, and jointing heat resistant metallic fibers 3 thereto by welding. The burner 1 is installed in a duct through which fluid to be heated, e.g. air, flows.