The invention relates to a cracking furnace containing a tubular vertical chamber which comprises an inlet for introducing a gas to be treated and an outlet for removing said gas from the chamber, means for heating said gas which include a heating tube extending vertically inside the chamber and coaxial with the chamber, the heating tube being shaped in such a way as to have a closed lower end and being arranged in such a way that the lower end thereof is arranged in the chamber and such that the upper end thereof is connected to a burner of the heating means arranged outside the chamber. The invention also relates to an assembly comprising such a cracking furnace and a device for thermal treatment of biomass and/or waste, an outlet of which is connected to the inlet of said cracking furnace.