A heat sink is provided with a box-like body attached to heat dissipating surface of a heat-dissipating element. A separation board separates the box-like body into upper and lower parts. A number of side separation boards divide the lower part into several areas, and nozzle parts are inserted into the side separation boards parallel to the attaching surface. Pin-like fins are formed in the bottom face in the several areas divided by the side separation boards and an air carrying means is provided at an upper area formed by the separation board for supplying cooling air to fins through the nozzle parts.