PURPOSE: To satisfactorily produce a biconical taper type star coupler by letting light enter from one end of optical fibers, measuring the exit light from other end and controlling the speed of expanding the holding spacing of optical fiber bundles and heating temperature.

CONSTITUTION: After a plurality of optical fiber bundles 28 are set to the optical fiber holders 21, 22 of a production unit 27, the heating element 28' of a heating unit 24 is provided between the holders 21, 22. Further, a light feeder 26 is coupled to enter light from the end part of at least one optical fiber and a detector 29 for measuring the exit light thereof is coupled to the other end part. Thereafter, the local portions of the fiber bundles 28 are heated by the heating element 28' and the spacing between the holders 21, 22 is gradually widened by the driving part 23. At this time, the way how the incident light of the optical fibers is coupled to the other fiber is discriminated through measurement of the exit light and the speed of widening the spacing of the holders 21, 22 and the heating temperature are controlled by a control part 25.