To provide a mixed combustion boiler device capable of being moved and installed on a place where a fuel can be effectively utilized, and easily operating a mixed combustion boiler to respond to safety processing of the mixed combustion boiler.

The comparatively-simple mixed combustion boiler device capable of holding down expensive equipment investment, is used. The fuel can be effectively utilized by a heavy fuel oil injection burner at the center of a furnace. Preferably, the heavy fuel oil injection burner is disposed above a burned material.