A printed wiring board has a heat transfer pattern facing a heat sink of an electronic component, on a first surface layer on which the electronic component having the heat sink is mounted. The printed wiring board has a through hole conductor formed in a through hole penetrating the printed wiring board corresponding to the heat transfer pattern, and thermally connected to the heat transfer pattern. The heat transfer pattern has a plurality of connecting lands exposed so as to be connectable to the heat sink of the electronic component by solder while being divided by a solder resist. The plurality of the connecting lands include lands adjacent to the through holes, and lands not adjacent to the through holes. The heat dissipation of the electronic component is enhanced while enhancing the connectability of the heat transfer pattern with the heat sink of the electronic component, at being mounted.