A printed circuit board is plated through the steps of providing a printed circuit board, covering at least a predetermined portion to be plated of the printed circuit board with a mask, sealing tightly the periphery of the concavity by sandwiching a sealing material between the mask and the circuit board, providing an electric contact piece, filling up the space with plating solution, connecting the electric contact piece to a power supply, and supplying a plating electric current to the predetermined portion to be plated of the printed circuit board.