A method and an apparatus for producing generator gas and activated carbon from solid fuels. A first gasification stage is supplied with fuel by an underfeed charging system and preheated air, the air and fuel being supplied in the same direction. In a second gasification stage and accompanied by the supply of secondary air, an intermediate gasification takes place. Finally, in a third gasification stage, the gas is reacted with glowing coke or charcoal, and the heat of the exiting gas is used for heating the air. The fuel centrally entering the first gasification stage is led from the inside to the outside and then upwards. Part of the entering fuel is precombusted in a precombustion chamber linked with the supply of the preheated air for reducing the oxygen content of the preheated air. In the intermediate gasification stage, the gas with the admixed air is passed through a Venturi nozzle or tube with a diffuser. The flue coal entrained from the first gasification stage is at least partly returned to the throat of the Venturi tube. The return is assisted both by vacuum in the Venturi tube and mechanically.