To provide a carbide mixing device and its method for mixing carbide obtained by carbonizing biomass as coal-alternative inexpensive fuel in a carbonizing furnace, and coal, and increasing a mixed combustion ratio of the carbide within a range allowable by a coal pulverizer.

This carbide mixing device comprising a carbide mixing means for mixing carbide, disposed on a means for conveying coal from a coal storage to a coal bunker by a conveyor, further conveying the coal to a coal pulverizer through a coal supplying machine to crush the coal into pulverized coal, and charging the same to a boiler, further comprises a means for pulverizing the carbide into a prescribed size, then sealing the same in a sealed container, and conveying the same by air current to a carbide hopper keeping a sealing state in storage, a means for temporarily holding the pulverized carbide in the carbide hopper, a means for supplying the carbide from the carbide hopper to an upstream side where a plurality of conveyors are connected in a state that end sides of the conveyors are vertically shifted from each other with difference in level between the conveyors, and a means for mixing the carbide and the coal by utilizing the difference in level between the conveyors.