PURPOSE: To obtain a method of burning a liquid mainly composed of heavy oil by recovering soots contained in a combustion exhaust gas and mixing these soots into the liquid fuel to burn the same.

CONSTITUTION: Soots 47 which have been entrapped by a dust collector 11 are introduced into a cyclone 35 and a bag filter 3 via a dust transporting line 46 by means of a dust transporting pump 34 so as to collect the soots 47 which are stored in a hopper 39 through lock valves 37 and 38, respectively. A predetermined quantity of the soots 47 are charged into a mixing tank 41 by means of a predetermined quantity supplier 40 provided at the lower part of the hopper 39, and mixed with a liquid fuel 48 for a slurry by a mixing 42 and slurried. A slurry 49 charged into a fuel line 14 is pressurized by an an atomizing pump 02 as a mixed fuel 50 and heated by a liquid fuel heater 40 until its viscosity has a predetermined value. Thereafter, it is sent into a liquid fuel burner 05 and mixed with an atomized medium 21 and injected into a furnace 08.