An air purifier including an air sterilizing unit, an air blowing unit arranged such that air flows in the air sterilizing unit; the air sterilizing unit comprising housing and an ultraviolet light emitting device which emits deep ultraviolet ray having wavelength of 200 to 350 nm; the housing comprising a sterilizing room; the sterilizing room comprising an air intake opening and an air outlet opening; and the ultraviolet light emitting device being arranged in the housing such that the deep ultraviolet ray is emitted toward inside of the sterilizing room, wherein (A) at least a part of an inner wall surface of the sterilizing room comprises an ultraviolet reflective material which may be covered with an ultraviolet ray transmitting material, and/or (B) one or more reflector plate is arranged in the sterilizing room.