NOVELTY - The steam boiler has a supply device (21) that is provided to supply raw materials of bio-fuel containing water, livestock farming waste materials, agricultural waste materials, forest waste materials, and dropping of livestock to a drying machine (20). The bio-fuel raw material is dried by the drying machine using hot combustion gas sent from a spark arrester (17), to obtain high calorie bio-fuel. The dust is collected from high calorie bio-fuel using dust collector (40), and dust-removed high calorie bio-fuel is stored in a high calorie bio-fuel storage silo (30).    USE - Steam boiler used for generating steam from bio-fuel, used in factory.    ADVANTAGE - Since the dust-removed high calorie bio-fuel is stored in the high calorie bio-fuel storage silo, the fixed quantity of high calorie bio-fuel can be supplied to the combustion furnace stably. Since the waste heat discharged from the steam boiler is utilized, the thermal efficiency of the steam boiler can be increased reliably, and the effective usage of the bio-fuel can be attained efficiently. Since the temperature of the bio-fuel is controlled by the spark arrestor, the occurrence of the fire outbreak accident or fire spark within drying machine can be prevented reliably. The cost of the steam boiler can be reduced efficiently by simplified structure.    DETAILED DESCRIPTION - The spark arrester is operated by letting combustion gas between the pebbles. The high calorie bio-fuel is quantitatively supplied to a combustion furnace (10) from the storage silo. The temperature of the high calorie bio-fuel is maintained to a temperature which is below the ignition temperature by the spark arrestor using a cold wind mixer (50).    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of the steam boiler.    Combustion furnace (10)    Spark arrester (17)    Drying machine (20)    Bio-fuel raw material supply device (21)    High calorie bio-fuel storage silo (30)    Dust collector (40)    Cold wind mixer (50)