An interposer substrate of the invention includes: a single substrate having a first main surface and a second main surface; a plurality of through-hole interconnections having at least a first portion formed so as to extend in a direction different from the thickness direction of the substrate, a second portion constituting one of end portions of a through-hole interconnection, and a third portion constituting the other of the end portions of the through-hole interconnection, the through-hole interconnections being provided inside the substrate so as to connect the first main surface to the second main surface, wherein the second portion is substantially perpendicular to the first main surface and is exposed to the first main surface, the third portion is substantially perpendicular to the second main surface and is exposed to the second main surface, and lengths of the through-hole interconnections are the same as each other.