PURPOSE: To prevent an outflow onto the surface of an inserting section of a binder, and to obviate deviation in an adapter by forming a projecting section movable in the axial direction to an external section fixed to the inner circumferential surface of the adapter of an internal light guide sleeve with the binder.

CONSTITUTION: 21a Is the projecting section, in which a section outer circumferential edge in a plane containing an axis of the internal light guide sleeve 21 takes an arcuate shape or a similar shape and an outer circumferential surface is in contact extending over the whole circumference of the circumferential direction in an inner circumferential surface on the through-hole 8 side of the adapter 9 and which is formed so as to be movable in the axial direction, in a section between a section soldered by a solder material 12 and a section, into which an aligning sleeve 15 is inserted, in the inner circumferential surface on the through-hole 8 side of the adapter 9 of the internal light guide sleeve 21. The aligning sleeve 15 can be inserted into the internal light guide sleeve 21 because the outflow onto the surface of the section, into which the aligning sleeve 15 of the internal light guide sleeve 21 is inserted, of the solder material 12 is prevented by the projecting section 21a when the internal light guide sleeve 21 is fixed to the inner circumferential surface of the adapter 9 by the solder material 12 in the structure of a magnetic sealing section to an insulating cylindrical body 4 of an internal light guide 10.