Provided is a printed circuit board that makes it possible for solder joining to be performed at a high yield even when extremely fine wiring is joined at an extremely narrow pitch and that makes the occurrence of a bridge between conductive joints less likely. A core wire 41 is mounted on a conductive joint 2 that has been subjected to preliminary soldering and the conductive joint 2 and the core wire 41 are covered by an optically transparent sheet 30. As a result, the core wire 41 is held in a mounted state on the conductive joint 2. While in this state, the optically transparent sheet 30 is irradiated with light. The preliminary solder 3 is heated and melted and the conductive joint 2 and the core wire 41 are joined.