Disclosed are a multilayer wiring board, which has a high degree of freedom of wiring design and can realize high-density wiring, and a method which can simply manufacture the multilayer wiring board. The multilayer wiring board comprises a core substrate and two or more wiring layers provided on the core substrate through an electrical insulating layer. The core substrate has a plurality of throughholes filled with an electroconductive material, and the front side and back side of the core substrate have been electrically conducted to each other by the electroconductive material. The throughholes have an opening diameter in the range of 10 to 100 μm. An insulation layer and an electroconductive material diffusion barrier layer are also provided, and the electroconductive material is filled into the throughholes through the insulation layer. A first wiring layer provided through an electrical insulating layer on the core substrate is connected to the electroconductive material filled into the throughhole through via.