PURPOSE: To effectively synthesize a small output, by forming the clad of one end part of plural optical fibers as one body, making it to almost the same thickness as its original optical fiber by prescribed length, and also making its tip thin.

CONSTITUTION: Light beams of semiconductor laser diodes LD1WLD4 are transmitted by single core optical fibers SOF1WSOF4 (part A), are transmitted in parallel to each other in a multioptical fiber MOF (part B), also pass through a part C whose diameter has been made thin, become plural parallel beams, pass through an optical lens LNS (part D), and are condensed onto the end face of an optical fiber OPC. Accordingly, a small output is synthesized effectively.