A method according to one embodiment includes steps of: preparing an optical module and optical fiber holding member; attaching a clip member to a receptacle of the optical module and the optical fiber holding member; and pressing the receptacle of the optical module and the optical fiber holding member from below and pressing the clip member from above. The pressing step has pressing the first flat surface of the receptacle and the second flat surface of the optical fiber holding member at the third flat surface of the clip member, and which performed until the first flat surface of the receptacle and the second flat surface of the optical fiber holding member establish parallelism with the third flat surface of the clip member by using a jig that changes the parallelism of the pressing surface.