According to one embodiment, a substrate includes a first dielectric substrate with a first through-hole, a second dielectric substrate with a first conductive via, a first signal line provided between the first dielectric substrate and the second dielectric substrate, a third dielectric substrate with a second conductive via, a first planar conductor provided between the second and third dielectric substrates and located away from the first and second conductive vias, a fourth dielectric substrate, and a second signal line provided between the third and fourth dielectric substrates. At least a part of a first inner wall of the first through-hole is not covered with a conductor. The first through-hole and the first conductive via partially overlap in a first direction. The first and second conductive vias partially overlap in the first direction. The second conductive via and the second signal line partially overlap in the first direction.