The invention relates to an optical detector for communication. The invention provides an optical detector for communication with simple structure capable of easily judging whether to have the use state of light transmission path visually by using non-visual light transmitted in the light transmission path and capable of detecting the errors of the optical detector for communication with high reliability and low cost. An optical detector for communication is connected with the ends of the light transmission path composed of optical fibers with a sleeve barrel, and detects whether to have the communication light of the light transmission path at the connecting part; and the optical detector for communication comprises: an optical detection jointing body installed on the connecting part of the sleeve barrel, connected with the ends of the light transmission path and having a core with an outer diameter different from that of the core of the light transmission path; and an optical detection part installed above the optical detection jointing body for detecting the communication light leaked through the optical detection jointing body.