A method for manufacturing a reliable multilayer wiring substrate at a relatively low cost having little or no warpage or distortion is provided. In certain embodiments an insulation core made of an insulation material that is more rigid than that of resin insulation layers is prepared. A through hole is formed through core upper and lower surfaces of the insulation core, and a through hole conductor is formed therein. A plate-like substrate is prepared, and resin insulation layers and at least one conductor layer are laminated on the substrate to form a first buildup layer. The insulation core is laminated on the first buildup layer so as to electrically connect the conductor layer and the through hole conductor. Resin insulation layers and at least one conductor layer are then laminated on the insulation core. Lastly, the substrate is separated from the first buildup layer to yield a multilayer wiring substrate.