Using scanning electron microscope, we studied the adult genital segments of pine needle gall midge, Thecodiplosis Japonensis, Uchida et Inouye Male: There were two pairs of hypoproct a pair of claspettes and aedeagus, Hypoproct were surrounded with many setae and sensilla. Clasperres which was projected below hypoproct was composed of two aegments and had many sensilla Aedeagus was long and flattened and possesed some sensilla at the terminal. Female :Ovipositor was segmented into three parts. Each segment had a different externla sturcture; particularly, the 2nd one was covered with reversed boat-like attachments and did not show any sensillum.