To provide a via filling method for filling a via with a prescribed amount of paste without leaving a non-filling area and for connecting layers with high yield.

The via filling method is provided with a process for applying paste in the through opening part of a transfer board having the through opening part formed in the same pattern as the via arrangement of a substrate, a process for repeating the filling process of paste to the through opening part again when paste is not filled in all the through opening parts, a process for bringing the transfer board where paste is filled in all the through opening parts close to the substrate in a vacuum atmosphere, and a process for increasing the pressure of the atmosphere in a state where the transfer board is closely brought close to the substrate and for differential pressure-filling paste filled in the through opening parts to the via.