The wiring board in the present invention includes: an insulating board; external connection pads for a differential signal and external connection pads for grounding or a power supply formed on a lower surface of the insulating board; and a through-conductor formed in the insulating board. Each of the external connection pads is formed in a two-dimensional arrangement, a diameter and an arrangement pitch of the external connection pad for a differential signal are smaller than a diameter and an arrangement pitch of the external connection pad for grounding or a power supply, and an arrangement pitch of the through-conductor connected to the external connection pad for a differential signal is less than or equal to an arrangement pitch of the external connection pad for a differential signal.