Ferrule, optical connector, and method for manufacturing optical connector

A ferrule (100) according to the present invention is provided with: a plurality of fiber holes (20) for causing a plurality of optical fibers (101a) to protrude, respectively, in a front end surface (100a); a plurality of fiber guide holes (25) communicating with back ends of the plurality of optical fiber holes (20) and being parallel to each other; and an optical fiber ribbon insertion hole (35) for inserting an optical fiber ribbon (101) of the plurality of optical fibers (101a) in a back end surface (100b) on the reverse side from one end surface. The ferrule (100) has a flange portion (30), and is provided with an internal space in which the plurality of fiber holes (20), the fiber guide holes (25), and the optical fiber ribbon insertion hole (35) communicate with each other, and provided with an adhesive filling window (55) for filling an adhesive (GL) into the internal space in only one surface of the flange portion (35).