A combined flow straightener and mixer is disclosed as well as a burner for a combustion chamber of a gas turbine having such a mixing device. At least two streamlined bodies are arranged in a structure comprising the side walls of the mixer. The leading edge area of each streamlined body has a profile, which is oriented parallel to a main flow direction prevailing at the leading edge position, and with reference to a central plane of the streamlined bodies, the trailing edges are provided with at least two lobes in opposite transverse directions. The periodic deflections forming the lobes from two adjacent streamlined bodies are out of phase.