It is intended to provide a sterilizer, an oral cavity sterilizer, a sterilization method, a sterilization apparatus, and a sterilizer evaluation method capable of enhancing a sterilization effect. The sterilizer including hydrogen peroxide and a catalase activity inhibitor containing scutellaria or green tea is brought into contact with a sterilization target. Next, the sterilization target is irradiated with light having a wavelength of 350 nm to 500 nm using a light emitting device formed of a semiconductor laser. By the light irradiation, the hydrogen peroxide is photolyzed to generate hydroxy radicals, and sterilization is achieved by the thus-generated hydroxy radicals.