An interposer 2 comprising a base 10 formed of a plurality of resin layers 26, 34, 42, 52, 56; a thin-film capacitor 12 buried in the base 10, including a lower electrode 20, a capacitor dielectric film 22 and an upper electrode 24; a first through-electrode 14b formed through the base 10 and electrically connected to the upper electrode 24 of the thin-film capacitor 12; and a second through-electrode 14a formed through the base 10 and electrically connected to the lower electrode 20 of the thin-film capacitor 12, further comprising: an interconnection 48 buried in the base 10 and electrically connected to the respective upper electrodes 24 of a plurality of the thin-film capacitors 12, a plurality of the first through-electrodes 14b being electrically connected to the upper electrodes 24 of said plurality of the thin-film capacitors 12 via the interconnection 48, and said plurality of the first through-electrodes 14b being electrically interconnected by the interconnections 48.