Provided are a sterilization system, an air conditioner, a sterilization method, and a sterilization program which make it possible to extend the life of a UV irradiation device and inhibit microorganisms in drain water. The sterilization system comprises an irradiation control unit that controls intermittent irradiation in which: irradiation is performed for an irradiation time that is not more than 22% of a reference time, said reference time being the time for which a prescribed sterilization rate is achieved when continuously irradiating drain water in a drain pan (3) of an air conditioner (1) with UV light from an LED (6); the irradiation is stopped for a prescribed pause time after the irradiation time; and irradiation is performed after the pause time.