A solid fuel burner comprising: a fuel nozzle comprising a flow passage through which a mixed fluid of solid fuel and a carrier gas thereof can flow, and an opening end portion (fs) on a furnace side; a combustion gas nozzle which is disposed on an outer peripheral side of the fuel nozzle to spray a combustion gas; a venturi provided in the fuel nozzle, in which the flow passage of the mixed fluid in the fuel nozzle is narrowed toward a center in a flow passage cross section; a fuel concentrator which is provided on the center side of the fuel nozzle to impart a velocity component to the mixed fluid in a direction away from the center of the fuel nozzle; and a flow passage partition member configured to partition the flow passage of the fuel nozzle into an inner side and an outer side in the flow passage cross section, wherein the flow passage partition member has a shape in which a cross-sectional area of an outer flow passage is enlarged toward a downstream end rather than an upstream end, the venturi at least has a contraction part in which a cross-sectional area of the flow passage of the mixed fluid is decreased toward the downstream side, and an expansion part disposed on the downstream side of the contraction part, in which the cross-sectional area of the flow passage of the mixed fluid is increased toward the downstream side, an upstream end of the fuel concentrator is provided between an upstream end and a downstream end of the expansion part of the venturi, and an inner diameter in the opening end portion (fs) of the fuel nozzle on the furnace side in the downstream end of the expansion part of the venturi is larger than an inner diameter in an upstream end of the venturi, characterized in that the cross-sectional areas of the flow passage of the mixed fluid are set so as to be monotonously increased or be the same as each other inside the fuel nozzle from the upstream end of the expansion part of the venturi to the opening end portion (fs) of the fuel nozzle on the furnace side. a fuel nozzle comprising a flow passage through which a mixed fluid of solid fuel and a carrier gas thereof can flow, and an opening end portion (fs) on a furnace side; a combustion gas nozzle which is disposed on an outer peripheral side of the fuel nozzle to spray a combustion gas; a venturi provided in the fuel nozzle, in which the flow passage of the mixed fluid in the fuel nozzle is narrowed toward a center in a flow passage cross section; a fuel concentrator which is provided on the center side of the fuel nozzle to impart a velocity component to the mixed fluid in a direction away from the center of the fuel nozzle; and a flow passage partition member configured to partition the flow passage of the fuel nozzle into an inner side and an outer side in the flow passage cross section, wherein the flow passage partition member has a shape in which a cross-sectional area of an outer flow passage is enlarged toward a downstream end rather than an upstream end, the venturi at least has a contraction part in which a cross-sectional area of the flow passage of the mixed fluid is decreased toward the downstream side, and an expansion part disposed on the downstream side of the contraction part, in which the cross-sectional area of the flow passage of the mixed fluid is increased toward the downstream side, an upstream end of the fuel concentrator is provided between an upstream end and a downstream end of the expansion part of the venturi, and an inner diameter in the opening end portion (fs) of the fuel nozzle on the furnace side in the downstream end of the expansion part of the venturi is larger than an inner diameter in an upstream end of the venturi, characterized in that the cross-sectional areas of the flow passage of the mixed fluid are set so as to be monotonously increased or be the same as each other inside the fuel nozzle from the upstream end of the expansion part of the venturi to the opening end portion (fs) of the fuel nozzle on the furnace side.