The core substrate is capable of securely preventing short circuit between an electrically conductive core section and a plated through-hole section. The core substrate comprises: an electrically conductive core section having a pilot hole, through which a plated through-hole section is formed; electrically conductive layers coating the inner face of the pilot hole and a surface of the core section; a gas purging hole being formed in the conductive layer coating the surface of the core section; an insulating material filling a space between the inner face of the pilot hole and an outer circumferential face of the plated through-hole section; and cable layers being laminated on both side faces of the core section.