Provided is a printed wiring board including a first heat dissipation pattern placed in one surface layer on which a semiconductor package is to be mounted, a second heat dissipation pattern placed in the other surface layer, and an inner layer conductor pattern placed in an inner layer, in which through holes are formed in the printed wiring board; the first heat dissipation pattern has a joint portion which is placed in an opposed region opposed to a heat sink of the semiconductor package and which is joined to the heat sink with solder; at least one of the through holes is placed in the opposed region; and the second heat dissipation pattern is formed in a pattern in which an end portion of a conductor film in the one of the through holes on the other surface layer side is separated.