Abstract: The invention has for its object a radiant flat flame burner used particularly in reheating furnaces for siderurgical purposes, which comprises in combination:a combustion air swirling device consisting of fixed flat blades, fitted in the combustion air annular duct, and adapted for imparting to the combustion air a swirling motion;a fire port of ceramic material, composed of a substantially cylindrical rear portion and of an adjoined flaring fore portion, delimited by a wall having a profile in form of a sector of a circle and extending over an angle of 90.degree.;a liquid fuel atomizing nozzle, the liquid fuel atomizing nozzle being provided with a swirling device, which is adapted for imparting a swirling motion to the atomized liquid fuel.