Provided is a boiler system (100) provided with: a boiler (10) for combusting fuel to generate combustion gas, the fuel containing less than 8.0% by weight of sulfur, less than 0.1% by weight of chlorine, and less than 20.0% by weight of water; a bag filter (20) for removing sulfur oxides and soot/dust; a denitrification unit (30) for removing nitrogen oxides; a desulfurization absorbent supply unit (40) for admixing a desulfurization absorbent into the combustion gas on the upstream side of the bag filter (20); and a refonner (50) for admixing a denitrification reducing agent into the combustion gas on the upstream side of the denitrification unit (30). The bag filter (20) performs dry desulfurization, the temperature of the combustion gas flowing through the bag filter (20) and into the denitrification unit (30) is kept above 200°C and no higher than 350°C, and the combustion gas from which sulfur oxides were removed by the bag filter (20) flows into the denitrification unit (30) without being heated on the upstream side of the denitrification unit (30).