Abstract: A portable burner (1) has a first (6) and a second mixer tube (18) for the delivery of primary and secondary air. To the first mixer tube belong an injector nozzle (2) for fuel gas and a spin producer (10). This first mixer tube (6) leads concentrically into the second mixer tube (18) larger in diameter, which has an inlet end (19) for the burner flame and aspiration points (20) for the secondary air. For the achievement of a thorough mixing of hot and cold gases and a low mixing temperature, between the outlet end (13) of the first mixer tube (6) and the inlet end (19) of the second mixer tube (18) there is disposed a filler body (16) filling the radial distance between the two tube ends and having a radial end face (21) from which the outlet end (13) of the first mixer tube (6) protrudes by a given amount "s." The aspiration points (20) for the secondary air are disposed exclusively in the area of the outlet end (13) of the first mixer tube (6) and aimed radially at the nozzle axis (A--A).