[Problem] To minimize transmission loss in spite of expansion and contraction of an adhesive in an adhesive-filled part. [Solution] The present invention is a ferrule for retaining the ends of optical fibers, wherein the invention is provided with a plurality of fiber holes lined up in a prescribed direction in order for optical fibers to be inserted therein, and an adhesive-filled part that is intended to be filled with an adhesive, the interior of the adhesive-filled part having an internal opening surface of the plurality of fiber holes, and a facing surface facing the opening surface. The adhesive-filled part has an upper-side opening surface that opens to the top surface, which is the surface on the side filled with the adhesive, and a lower-side opening surface that opens to the bottom surface, which is the surface on the side opposite to the top surface.