An electronic component unit includes: first electronic components which do not need to be cooled; second electronic components which are cooled; a first circuit board in which the first electronic component is mounted on a first surface and in which the second electronic component is mounted on a second surface; a second circuit board in which the first electronic component is mounted on a first surface and in which the second electronic component is mounted on a second surface; and one cooling plate which includes a first cooling surface and a second cooling surface, the second electronic component mounted on the second surface of the first circuit board is cooled by contact with the first cooling surface of the cooling plate, and the second electronic component mounted on the second surface of the second circuit board is cooled by contact with the second cooling surface of the cooling plate.