An inductor built-in substrate includes a core substrate having openings and first through holes formed therein, a magnetic resin filling the openings and having second through holes formed therein, first through-hole conductors formed in the first through holes respectively such that each of the first through-hole conductors includes an electroless plating film and an electrolytic plating film, and second through-hole conductors formed in the second through holes respectively such that each of the second through-hole conductors includes an electroless plating film and an electrolytic plating film. The first through-hole conductors and the second through-hole conductors are formed such that a thickness of the electroless plating film in the first through-hole conductors is larger than a thickness of the electroless plating film in the second through-hole conductors.