PROBLEM TO BE SOLVED: To provide a filter sterilizer for an air conditioner which is easy to assemble, adjust, and maintain, and in which sterilizing effects of ultraviolet rays emitted by an ultraviolet ray source are improved by scanning an absorbing surface of an HEPA (High Efficiency Particulate Air) filter without requiring a drive mechanism such as a motor.SOLUTION: An ultraviolet ray source 10 is placed near a side edge of an absorbing surface 5A of the HEPA filter 5 inside an air cleaner 1 and an impeller 11 rotated by the air flow absorbed by the HEPA filter 5 is placed at a position near the absorbing surface 5A. The impeller 11 includes a plurality of rotary blades each of which has at least a partial mirror surface that reflects ultraviolet rays radiated by the ultraviolet ray source 10 toward the absorbing surface 5A, and the ultraviolet rays reflected on the mirror surface scan the absorbing surface 5A of the HEPA filter as the impeller 11 rotates, and sterilizes the absorbing surface 5A.
