A printed wiring board has a packaging substrate having multiple pads, and a transmission substrate mounted on the multiple pads of the packaging substrate. The packaging substrate has a pad group constituted of pads which mount an electronic component, the multiple pads mounting the transmission substrate includes a first pad positioned in a peripheral portion of the packaging substrate and a second pad positioned between the first pad and the pad group, the second pad is electrically connected to a signal pad of the pads in the pad group, and the transmission substrate includes a horizontal wiring which electrically connects the second pad and the first pad and which transmits a signal between the second pad and the first pad.