PURPOSE: To exactly make an optical output laser beam incident on the inside of the core of an optical fiber by adjusting the optical axis of a high output laser beam and the axial line of the end face of the optical fiber so as to be positioned on a straight line.

CONSTITUTION: The high output laser beam emitted from a laser source 1 is transmitted through a shading means 2, and converged on the end face of an optical fiber 4 by a condenser lens 3. The end face 9 of the optical fiber 4 is positioned by a positioning device 6. A power meter 5 detects the light receiving amount of the laser beam on the end face 9 of the optical fiber 4. Next, the end face 9 of the optical fiber 4 is positioned so that the light receiving amounts of the power meter 5 can be the maximum, and the optical axis of the laser beam and axial line of the end face 9 of the optical fiber 4 are adjusted so as to be positioned on the straight line. The optical output laser beam can be exactly made incident on the inside of the core of the optical fiber 4 by moving the shading means 2 in a direction M by a moving means.