A board unit comprises a board, a heat generating component mounted on a front surface of the board, a first heat transfer plate whose inner surface faces the front surface of the board and is received by the heat generating component, a heat insulating material that is superimposed on an outer surface of the first heat transfer plate and that insulates heat dissipation, a second heat transfer plate that continues to the first heat transfer plate and that defines a heat conducting surface and a heat receiver that is received by the heat conducting surface of the second heat transfer plate and that defines a flow path of a coolant.