To supply a solid biomass fuel to be burned while mixed with coal, even when hard biomass particulate pieces are mixed in the solid biomass.

The solid biomass is separated into fine power particles and particulate pieces which can not be ground by a coal grinder by a separating device 11, and the particulate pieces separated by the separating device 11 is finely ground by a biomass grinder 13. A solid biomass fuel charging system 12 mixes the solid biomass fine powder particles separated by the separating device 11 and the fine powder particles of the particulate pieces ground by the biomass grinder 13 to prepare the solid biomass fuel, and puts the solid biomass fuel into a coal supply line 14 for supplying coal.