A light emitting unit A includes a base member 1, a holder 3 for holding a laser diode 7 and a coupling tool 5 which is a leaf spring material. A pair of circular surfaces 32, 32 of the holder 3 are respectively abutted on a pair of flat surfaces 14, 14 of the base member 1 on the overlapping place of the base member 1 and the holder 3. The center axis line of the circular surfaces 32, 32 coincides with a center axis line O passing the light emission point P of the laser diode 7. Projected pieces 55, 55 of the coupling tool are elastically contacted with the laser diode at the back of the center axis line O.