PURPOSE: To simultaneously adjust an optical axis in the case of adjusting and fixing plural optical fibers with respect to one optical device, to restrain the deterioration in transmission characteristic and to improve workability.

CONSTITUTION: The optical device 3 is fixed to a fixing jig 4, the optical fiber (A) 1 is fixed to an upper optical fiber adjusting unit 5, and the optical fiber (B) 2 is fixed to a lower optical fiber adjusting unit 6. With the fixing jig 4 as a reference, the optical axis is optimally adjusted for the optical fiber (B) 2 fixed to the lower optical fiber adjusting unit 6 with respect to the optical device 3. The fixing jig 4 and the unit 6 are treated as one unit, and the optical axis is optimally adjusted for the optical fiber (A) 1 fixed to the unit 5 while keeping a condition where the positional relation between the optical device 3 and the lower optical fiber (B) 2 are kept on a stage for center adjustment.