To allow a burner to release a large amount of radiant heat with a reduction in NOx emission by a method wherein a second porous radiation layer having a porosity higher than that of a first layer is provided at a distance from the first layer and a combustion zone is formed between the two layers.

An air-fuel mixture 021 is sent into a fuel mixing plenum chamber 10 by a blower 17, flows through a porous structure of a first layer incorporating a perforated metal plate 11 and a flexible porous layer 12 and is ignited on the surface of a radiation-stabilizing layer 13 of a second porous structure so that a flame front is produced in a gap 15 or on the surface of the radiation- stabilizing layer 13. A radiation-stabilizer made up of the porous radiation- stabilizing layer 13 of a high-temperature metallic screen, a ceramic structure or a composite structure begins to emit light energy and cools down the flame zone so that the temperature in the flame zone drops and the NOx emission is restrained.