To completely form a sterilizing space by controlling the output to optically set the emission and irradiation diameter of applied ultraviolet rays.

At the time of operation, a device is carried to an operation room, and an irradiation part 27 is applied to the region to be operated. An optical system part 5 having an irradiation diameter suitable for operation is selected and installed on the tip of the lamp part 3. Subsequently, LD 54 is lighted and the irradiation range is accurately adjusted to the region to be operated and set. An ultraviolet ray generating lamp 49 is lighted. Thus, the ultraviolet rays can be applied to the irradiation range determined by the optical system part 5, and a sterilizing space is formed in the region to be operated. By this arrangement, the region to be operated can be sterilized instantaneously and the irradiated space can be kept in the aseptic condition.