A module board of an embodiment includes a printed board having a through-hole, a semiconductor device mounted on the printed board so as to cover the through-hole, and a heat conductive polygonal column included in the through-hole. The semiconductor device includes a ground terminal or a power supply terminal, the polygonal column is supported by the through-hole at the corners of the polygonal column, and the polygonal column is connected to the ground terminal or the power supply terminal.