A printed wiring board including: a first substrate on which a plurality of pads to be connected to a connector is arranged to form a front array and a rear array in two rows; a second substrate that is laminated on the first substrate and formed with first wirings connected to first pads of the front array and second wirings connected through vias to second pads of the rear array; engageable parts that are to be engaged with engagement parts of the connector; and one or more reinforcement layers that are provided at the frontward side in the connecting direction than the engageable parts of the first substrate and/or the second substrate. The wirings each have a part formed to have a constant width along the inserting direction to the connector and an expanded-width part expanded to have a wider width than the constant width in the inserting direction of the connector.