PURPOSE: To enable firing with pulverized coal in a double cylindrical upright firing furnace for a liquid fuel use by a method wherein pulverized coal is delivered by a a constant quantity, transported by pneumatic transport in a preset air ratio and is blown into a burner.

CONSTITUTION: The pulverized coal delivered by means of a constant quantity delivering system attached with a weight and volume meter 5 is carried from an injector 6 to a cyclone 8'. In said cyclone 8', the pulverized coal is separated from air and is stored in a service hopper 10. The pulverized coal stored thereat is delivered by a constant quantity delivering system 10' and is placed in an injector 12. The pulverized coal placed in the injector 12 is sent by the pressure of a blowing fan 13 to a burner 24 to be mixed with heavy oil and the air for atomization. The mixture is burnt by being ignited in the burner 24 and is injected into the combustion chamber 2 of a furnace main body 1 together with the secondary air. By means of this combustion gas, a material to be burnt in the furnace main body 1 is burnt.