An apparatus for generating energy by gasification, comprising an updraft gasifier provided with a main body that is internally hollow so as to define a reaction chamber into which are fed a flow of combustible material and a flow of a first oxidizer medium, and with a substantially boxlike supporting body that is arranged outside the main body, the apparatus further comprising elements for the combustion of a synthesis gas mixed with a flow of a second oxidizer medium, the gasifier comprising separation elements interposed between the supporting body and the main body so as to define a first chamber for introducing the first oxidizer medium, connected to the reaction chamber, and a second chamber for introducing the second oxidizer medium, respective first and second adjustable elements for supplying the first and second oxidizer.