A wiring board has a first rigid wiring board having an accommodation portion, a second rigid wiring board accommodated in the accommodation portion, an insulation layer formed over the first rigid wiring board and the second rigid wiring board, and a joint conductor extending in a direction from a first surface of the first rigid wiring board to a second surface of the first rigid wiring board on the opposite side of the first surface of the first rigid wiring board such that the joint conductor is penetrating through the boundary between the first rigid wiring board and the second rigid wiring board and joining the first rigid wiring board and the second rigid wiring board.