A combustion apparatus provided with a burner includes a fuel injection nozzle disposed rearward of a gas passable solid and a pre-mixture region between a downstream end of the solid and the fuel injection nozzle. The gas passable solid may be of a straightener type. Air for combustion includes main air and pilot air separated from each other. The apparatus may be coupled to each end of a radiant tube. The apparatus may be provided to a direct and indirect combustion type thermal facilities.