PURPOSE: To prevent peeling owing to shrinkage on curing of an adhesive agent by taking an adhering surface on the direction where the resin adhesive agent shrinks on curing as well as to enable increase in resistance to moisture permeation by sealing at two points on both high and low pressure side.

CONSTITUTION: A structure of a sealing part for an optical fiber is provided with a metallic block 13 which is attached to the wall 10 of a case while maintaining airtightness with an O-ring 14, etc. and has a through-hole for insertion of an optical fiber 16 and collars 13a, 13'a in the outlets on both sides of said hole and a core metal 17 which can be inserted together with the optical fiber into the hole of said block 13. The fiber 16 is plced along the metal 17 and is held inserted together with the core metal into the hole of the block 13. A resin adhesive agent 18 is built up in this state on the outside surface of the collars 13a, 13'a at both ends of the hole and the outside circumference of the metal 17. The fiber 16 is embedded into said agent 18 and is thus fixed.