In a method of manufacturing a circuit substrate of the present invention, a first through hole is formed in a semiconductor substrate and a first insulating layer is formed on the entire surface of the semiconductor substrate, and then first wiring layers connected to each other via an outer through conducting portion provided on the inner surface of the first through hole are formed on both sides of the semiconductor substrate, and then a second insulating layer is formed which covers the first wiring layers on both sides of the semiconductor substrate and the outer through conducting portion on the inner surface of the first through hole, the second insulating layer has a structure in which a second through hole is provided in a central portion of the first through hole, and then second wiring layers connected to each other via an inner through conducting portion provided in the second through hole are formed on the second insulating layer on both sides of the semiconductor substrate.