A plug-in board replacement method includes preparing a board having a piece board, forming first conductive pattern on first surface of the board, forming second conductive pattern on second surface on the opposite side such that the second pattern is on the opposite side of the first pattern, irradiating laser upon the first and second surfaces along the first and second patterns such that the piece is cut out from the board, and fitting the piece into another board. The irradiating includes irradiating laser upon the first surface along the first pattern such that laser is irradiated along the border between edge portion of the first pattern and the first surface and laser upon the second surface along the second pattern such that laser is irradiated along the border between edge portion of the second pattern and the second surface such that the piece is cut out through the board.