PURPOSE: To prevent inclusion of foam to the inside or generation of a phenomenon resembling to boiling by heating the end faces of optical fibers by electric discharge and projecting cores to bring first the central part of the end faces into contact with each other then adjusting the moving speed so as to expand gradually the contact region toward the circumference.

CONSTITUTION: A pair of optical fibers to be connected are opposed and axially aligned in such a way that electric discharge electrodes 10, 10' are brought approximately to the center. After the space between the end faces is maintained adequately, the movement of the fibers 11, 11' is started at the same instant when the electric discharge is started. The discharge voltage is approximately constant if the shape of the electrodes and the space between the electrodes are the same and therefore the discharge current, the space between the optical fibers and the moving speed of the optical fibers are so adjusted and set that the end faces of the cores project more than the end faces of the clads just before the end faces of the optical fibers contact with each other. The fibers 11, 11' are further forcibly pushed to each other after the contact of the end faces and thereafter the movement thereof, then the discharge are stopped to complete the connection.