A biomass feeding unit feeds biomass to a boiler. A hydrogen-chlorine monitoring unit measures hydrogen-chloride content in flue gas fed to a desulfurization equipment. A mercury monitoring unit measures mercury content in treated flue gas emitted from the desulfurization equipment. A feed-amount instruction unit instructs proper feed amount of the biomass to the biomass feeding unit based on measurement values obtained by the hydrogen-chlorine monitoring unit and the mercury monitoring unit.