A lean-rich burner is provided, in which an air-rich flame and a fuel-rich flame are formed by a simple structure, thereby reducing the emission of noxious gas and enabling stable combustion. The lean-rich burner includes: a main flame part (110) for burning a fuel-rich mixture in which primary air, which is some of air supplied by a blower, and fuel are mixed; auxiliary flame parts (120) installed on left and right sides of the main flame part (110) to burn an air-rich mixture; a main mixture channel (130) for supplying the fuel-rich mixture to the main flame part (110); a mixture distribution hole (140) formed along the main mixture channel (130) to supply some of the mixture flowing along the main mixture channel (130) to the auxiliary flame parts (120); and a Venturi part (150) having a Venturi structure in which secondary air inflow holes (151) are formed to mix secondary air, which is some of the air supplied by the blower, with the mixture introduced through the mixture distribution hole (140).