PURPOSE: To provide a terminal structure of optical transmission line which does not adversely affect an apparatus, etc., such as connecting box at the terminal of the optical transmission line even if a plastic pipe constituting the optical transmission line receives an accident, such as failure.

CONSTITUTION: An optical fiber unit 3 led out of the terminal of the plastic pipe 2 of an optical transmission line 1 having the optical fiber unit 3 inserted into the plastic pipe 2 is sealed by a waterstopping boot 3 having a slit 10 at the terminal of the plastic fiber 2. As a result, an apparatus, etc., such as connecting box at the terminal of the optical transmission line 1 are not adversely affected by soaking even if the plastic pipe 2 receives an accident, such as failure. The optical fiber unit in the plastic pipe 2 is not adversely affected even if the accident, such as water-intrusion, conversely arises in the apparatus, etc., such as connecting box at the terminal of the optical transmission line 1.