PURPOSE: To prevent laser light from being irradiated to a hoder by prescribing an emitting end part of a transmission line of the laser light by a reflecting surface constituted so that its diameter becomes gradually larger as it approaches the emitting end.

CONSTITUTION: An optical fiber 1 and a condenser lens 2 are held by a holder 3, and a hollow cylindrical body 4 is placed on an emitting end of the optical fiber 1. This hollow cylindrical body 4 has an inside surface 5 of a high reflection factor, and this inside surface 5 constitues a transmission line of laser light emitted from the optical fiber 1. As for the inside surface 5 of the hollow cylindrical body 4, the diameter of an outlet part for sending out the laser light is made larger than the diameter of an inlet part for receiving the laser light. Therefore, an emitting end part of the transmission line of the laser light is prescribed by the reflecting surface 5 constituted so that its diameter becomes gradually larger as it approaches the emitting end.