PURPOSE: To provide a small size and light weight heat radiator assuring radiation of a large amount of heat per unit area by forming a large number of projections to at least one surface, except for the heating generating element mounting position, of a heat radiator for a heat generating element.

CONSTITUTION: A heat radiator 9 is provided, at its one surface, with many projections 2 except for the element mounting position. Each projection 2 is provided with a hole 3 provided up to the rear surface of the heat radiator 9. Thereby, the total front surface area per unit area of the heat radiator 9 becomes large and the amount of heat radiated per unit volume becomes larger than that of the related art. Since height of the projection 2 is lower than that of the heat radiating fin of the related art, size in the plate thickness direction of the heat radiator 9 can be reduced as much, resulting in no fear for lowering element mounting density in the printed circuit board. Therefore, an electronic circuit device constituted by using the heat radiator 9 can be completed small in size and light weight with the sophisticated function.