To decrease an insertion loss by shortening an optical path length between an input side optical fiber and an output side optical fiber, and to decrease a stroke of a drive component. Input side optical fibers and a preliminary optical fiber arranged in parallel to one another and output side optical fibers arranged in parallel to one another are arranged in two stages, and a fixed prism 14 is arranged to be opposite to end surfaces of these. A preliminary optical fiber prism 15b is provided on one oblique surface of the fixed prism 14 to be opposite to a preliminary optical fiber 20, and a driven prism 15a can be made to come in contact with and separated from the one oblique surface of the fixed prism 14, and the driven prism 15a can be moved along the input side optical fibers. At a position where the driven prism 15a comes in contact with the oblique surface of the fixed prism 14, outgoing light from the input side optical fiber is not totally reflected at the oblique surface of the fixed prism 14, but is incident on the driven prism 15a, and after it is sent from the driven prism 15a to the preliminary optical fiber prism 15b, it is incident on the preliminary optical fiber 20 from the preliminary optical fiber prism 15b.