A printed wiring board according to an embodiment includes a wiring board body, a first connection part and a second connection part. In the first connection part, a heat-receiving front surface is a first land formed on a front surface of the wiring board body. A heat-receiving back surface is formed on a back surface of the wiring board body. A main-heat conducting part is a through-hole that inter-connects the heat-receiving front surface and the heat-receiving back surface. In the second connection part, a second land is formed on the front surface of the wiring board body. The second land is not connected to any conductor pattern formed on the back surface of the wiring board body.