An interposer includes a first insulating layer made of an inorganic material and having a first land, a second land and a first wiring electrically connecting the first land and the second land, and a second insulating layer formed over a first surface of the first insulating layer and having a second wiring, a second pad for loading a second electronic component over the second insulating layer and a first via conductor electrically connecting the second land and the second wire. The first wiring and the second wiring electrically connect the first land and the second pad. The first land and second land are positioned such that a first electronic component is mounted over a second surface of the first insulating layer on the opposite side of the first surface. The second wiring has a longer wiring length and a greater thickness than the first wiring.