An interposer includes a plurality of identical functional blocks arranged in the x direction, for example, and the functional blocks include a first region mounting a semiconductor chip, a second region mounting a light emitting element chip, a third region mounting a light receiving element chip, and a plurality of silicon waveguides. Then, the second and third regions are arranged between the first region and a first side along the x direction of the interposer. In addition, the plurality of silicon waveguides are arranged between the second region and the first side, and between the third region and the first side, extending from the second region toward the first side and from the third region toward the first side and are not formed between the functional blocks adjacent in the x direction.