Electronic components differing in height (a CPU 2a, a capacitor 2b, and coil elements 2c) are mounted on a printed circuit board 1. A heat-absorbing member 3 is provided above the printed circuit board 1 in such a way that the member 3 contacts not only the top surface of the CPU 2a that is the shortest but the sides of the capacitor 2b and the coil elements 2c. To circulate a cooling medium, a flow path 4 is formed in the heat-absorbing member 3. Heat generated at the CPU 2a is transmitted from its top surface to the cooling medium in the flow path 4 via the heat-absorbing member 3; heat generated at the capacitor 2b and the coil elements 2c is transmitted from their sides to the cooling medium in the flow path 4 via the heat-absorbing member 3.