The present invention relates to a positioning system for automatically positioning and attaching at least one optical fiber inserted into said positioning system along a predetermined optical axis. This positioning system comprises a base member with a flat upper surface and a V-shaped reception channel which is parallel to the upper surface and is formed therein for receiving at least one optical fiber. This system also includes a spring-effect retaining member which is mounted on the upper surface of the base member for maintaining the at least one optical fiber inserted into the reception channel. This invention provides for a simple structure, as well as, for a precise and mechanically resistant coupling since the retaining member comprises a membrane which is parallel to the upper surface of the base member, which is mounted above the reception channel and which can be resiliently diverted in a direction perpendicular to the upper surface of said base member. When the at least one optical fiber is inserted into the reception channel, the membrane is diverted so as to fix said optical fiber in the reception channel due to the restoring force of the membrane.