Rich-lean flame burner

A rich-lean flame burner comprising on an upper part thereof:

• a longitudinally elongated lean burner port for ejecting a lean air-fuel mixture whose fuel concentration is leaner than a theoretical air fuel ratio;
• and a rich burner port lying adjacent to at least one lateral side of the lean burner port with a clearance of a predetermined lateral width for ejecting a rich air-fuel mixture richer than the theoretical air fuel ratio;
• the rich-lean flame burner further comprising:
• a straightening member having a plurality of straightening plates for dividing the lean burner port into a plurality of laterally sectioned regions;
• and, at a plurality of longitudinal points of the straightening member, first constricted portions by bringing the plurality of straightening plates into close contact with one another, at upper parts of the straightening plates, so as to divide the lean burner port into a plurality of longitudinally divided portions,
• wherein at least the laterally outermost straightening plate adjacent to the clearance is provided with second constricted portions which, in close contact with the straightening plate adjacent to the laterally outermost straightening plate, divide each of such portions of the lean burner port as have been divided by the first constricted portions into a plurality of longitudinally divided portions, and wherein the second constricted portions are such that the lower ends thereof are positioned above the lower ends of the first constricted portions and that a vertical length of the second constricted portions is shorter than the first constricted portions, and
• wherein the plurality of straightening plates are provided with the second constricted portions, upper ends of the second constricted portions disposed at least in part of the plurality of straightening plates are positioned below the upper ends of the straightening plates.