To stably burn the pyrolytic gas without being affected by the fluctuation in generation of the flammable dust in a secondary combustion method of the pyrolytic gas of the waste generated in treatment of wastes.

In a secondary combustion method of the pyrolytic gas containing the flammable dust generated in the partial combustion of wastes, the dust in the pyrolytic gas containing the flammable dust is collected by a dust remover provided in the middle of a gas duct to lead the pyrolytic gas containing the flammable gas into a secondary combustion furnace 6, and then, the pyrolytic gas is blown from a burner 7 of the secondary combustion furnace 6 and burned in a primary combustion zone 9, and the flammable dust collected by the dust remover is stored in a hopper, and the flammable dust taken from the hopper is fed to a secondary combustion zone 10 together with the air and burned there.