A concentrate burner for feeding a pulverous concentrate mixture and reaction gas into the reaction shaft (1) of a flash smelting furnace. The concentrate burner includes a feeder pipe (2) for feeding the concentrate mixture into the reaction shaft (1), the orifice (3) of the feeder pipe opening to the reaction shaft, a dispersing device (4), which is arranged concentrically inside the feeder pipe (2) and which extends to a distance from the orifice inside the reaction shaft (1) for directing dispersing gas to the concentrate mixture flowing around the dispersing device. For feeding the reaction gas into the reaction shaft (1), a gas supply device (5) includes a reaction gas chamber (6), which is located outside the reaction shaft and opens to the reaction shaft (1) through an annular discharge orifice (7) that surrounds the feeder pipe (2) concentrically for mixing the reaction gas discharging from the discharge orifice with the concentrate mixture discharging from the middle of the feeder pipe, the concentrate mixture being directed to the side by means of the dispersing gas. The reaction gas chamber (6) comprises a turbulent flow chamber, to which an inlet channel (9) opens tangentially for directing the reaction gas to the reaction gas chamber in a tangential direction. In the inlet channel (9), an adjusting member (11) is arranged for adjusting the cross-sectional area of the reaction gas flow.