A printed board joining method according to an embodiment includes preparing a printed board having, on an upper surface, a plurality of connection land portions provided along a side end, preparing a printed board having, on a lower surface, a plurality of connection land portions along a side end, and joining the printed board and the printed board together with a conductive joining material such that the upper surface is opposed to the lower surface and the plurality of connection land portions are electrically connected to the corresponding connection land portions. One or more cutout portions are provided between the plurality of connection land portions and/or between the plurality of connection land portions.