A combustion apparatus 1 includes an intermediate member 6 constituted by a premixer 2 and a burner port assembly 3 and an air passage member 5, the intermediate member 6 being interposed between two air passage members 5. Fuel gas flows into an opening row part 10. The opening row part 10 has a number of openings 8 arranged linearly, so that the fuel gas introduced into the row part 10 is uniformly discharged through each of the openings 8. The fuel gas discharged through the openings 8 of the row part 10 bumps into air at mixing spaces 39. Fuel gas discharged through slots is homogenous and uniform in flow rate. Fuel gas produces a primary flame in a first combustion part 46 to perform a primary combustion. Unburned combustible components are discharged outside through openings of the first combustion part 46 and produce a secondary flame with air supplied through the distal end portion of the air passage member 5.