A boiler (19) is provided with: a combustion furnace (10); an exhaust gas passage (28) through which the combustion exhaust gas from the combustion furnace (10) passes; a superheater tube (27) which is provided within the exhaust gas passage (28); and a corrosion inhibition device (59) which supplies a corrosion inhibitor for boilers into the exhaust gas passage (28). The corrosion inhibitor for boilers is used for the purpose of inhibiting corrosion of the superheater tube (27), and contains corrosion inhibition particles which adhere to the superheater tube (27) together with the combustion ash floating within the exhaust gas passage (28) and attract corrosive particles in the combustion ash thereto.