An upper board having an opening and forming a circuit on a surface layer, a connection sheet between boards having an opening and forming conductive holes filled with conductive paste in through-holes, and a lower board forming a circuit on a surface layer are stacked up, heated and pressed. In particular, the connection sheet between boards is made of a material different from the upper board and the lower board. A multi-layer circuit board having a cavity structure, and a full-layer IVH structure with high interlayer connection reliability can be manufactured.