A sterilization treatment device and a sterilization treatment method that do not require accurate measurement of the weight of the sterilization liquid. The sterilization treatment device is an atomization unit for atomizing a sterilization liquid containing an active ingredient, and a supply unit for supplying the sterilization liquid atomized by the atomization unit to a sterilization treatment target space for sterilization treatment. And a relative humidity measuring unit for measuring the relative humidity inside the sterilization target space. The amount of sterilization liquid is supplied to the sterilization treatment target space until the relative humidity becomes equal to or higher than the set value, and then the amount of sterilization liquid is supplied according to the degree of sterilization inside the sterilization treatment target space. The supply of the sterilization solution is controlled so that the supply is performed to the sterilization target space.減菌液の重量を正確に測定する必要のない減菌処理装置及び減菌処理方法を提供する。減菌処理装置は、有効成分を含む減菌液を霧化する霧化ユニットと、霧化ユニットによって霧化された減菌液を、減菌処理を行う減菌処理対象空間に供給する供給ユニットと、減菌処理対象空間の内部の相対湿度を測定する相対湿度測定部とを有している。相対湿度が設定値以上となるまでの量の減菌液の供給を減菌処理対象空間へ行い、その後、減菌処理対象空間の内部での減菌の程度に応じた量の減菌液の供給を減菌処理対象空間へ行うように、減菌液の供給の制御が行われる。
