A wiring board includes a main surface where an electronic component is mounted in a face-down manner so that a surface of the electronic component having plurality of external connecting terminals faces the main surface of the wiring board, the electronic component being fixed to the wiring board by an adhesive; an insulating layer formed on the main surface where the electronic component is mounted; an opening part formed in the insulating layer so that a plurality of adjacent wiring patterns are commonly and partially opened, the adjacent wiring patterns having electrodes where electrodes of the electronic component are connected; wherein an outer periphery of the opening part situated at a center side of the wiring board is formed in an oblique direction against extending directions of the wiring patterns.