A concentrate burner for feeding a pulverous concentrate mixture and reaction gas into the reaction shaft of a flash smelting furnace, comprising - a feeder pipe for feeding the concentrate mixture into the reaction shaft, the orifice of the feeder pipe opening to the reaction shaft, - a dispersing device, which is concentrically arranged inside the feeder pipe and which extends to a distance from the orifice inside the reaction shaft, for directing dispersing gas to the concentrate mixture that flows around the dispersing device, - a gas supply device for feeding the reaction gas into the reaction shaft, the gas supply device including a reaction gas chamber, which is outside the reaction shaft and opens to the reaction shaft through an annular discharge orifice that surrounds the feeder pipe concentrically for mixing the reaction gas discharging from the discharge orifice with the pulverous solid matter discharging from the middle of the feeder pipe, the solid matter being directed sideward by means of the dispersing gas, the reaction gas chamber being formed into a turbulent flow chamber to provide a turbulent flow of the reaction gas discharging from the discharge orifice, an inlet channel opening tangentially to the reaction gas chamber for directing the reaction gas to the reaction gas chamber in a tangential direction, characterized in that an adjusting member is arranged in the inlet channel for adjusting the cross-sectional area of the reaction gas flow, and in that the reaction gas chamber includes a cylindrical upper part, to which the inlet channel tangentially opens, and a conical lower part, which converges conically from the cylindrical upper part down towards the discharge orifice. - a feeder pipe for feeding the concentrate mixture into the reaction shaft, the orifice of the feeder pipe opening to the reaction shaft, - a dispersing device, which is concentrically arranged inside the feeder pipe and which extends to a distance from the orifice inside the reaction shaft, for directing dispersing gas to the concentrate mixture that flows around the dispersing device, - a gas supply device for feeding the reaction gas into the reaction shaft, the gas supply device including a reaction gas chamber, which is outside the reaction shaft and opens to the reaction shaft through an annular discharge orifice that surrounds the feeder pipe concentrically for mixing the reaction gas discharging from the discharge orifice with the pulverous solid matter discharging from the middle of the feeder pipe, the solid matter being directed sideward by means of the dispersing gas, the reaction gas chamber being formed into a turbulent flow chamber to provide a turbulent flow of the reaction gas discharging from the discharge orifice, an inlet channel opening tangentially to the reaction gas chamber for directing the reaction gas to the reaction gas chamber in a tangential direction, characterized in that an adjusting member is arranged in the inlet channel for adjusting the cross-sectional area of the reaction gas flow, and in that the reaction gas chamber includes a cylindrical upper part, to which the inlet channel tangentially opens, and a conical lower part, which converges conically from the cylindrical upper part down towards the discharge orifice.