Abstract: A printed circuit base board comprising an insulating substrate having a thin electric circuit layer composed of an electrically conductive material on one surface is disclosed. This printed circuit base board is drilled at parts of the insulating substrate contiguous to component lead attaching land-forming portions of the electric circuit layer from the opposite surface of the printed circuit base board, while leaving the land-forming portions undrilled, so that composite lead-inserting holes having a size sufficient to insert component leads exactly therein and having one end closed on the side of the land-forming portions of the electric circuit layer and the other end opened are formed.