A disclosed apparatus includes: a vessel accommodating an object to be treated； an ultraviolet ray lamp that emits ultraviolet rays to the object to be treated； a control unit accommodating circuit equipment that controls energization of the ultraviolet ray lamp； and two (i.e., first and second) fans disposed in series with each other in an exhaust opening, formed in a casing of the control unit, for cooling the circuit equipment within the control unit. While the apparatus is in operation, the first fan is normally kept in a driven state and an air flow exhausted by the first fan passes through the second fan while idling the second fan. The apparatus further includes an abnormality detector that detects an abnormality of the first fan, such that the second fan is activated in response to the abnormality of the first fan being detected by the abnormality detector.
