To provide a heat sink capable of enhancing radiation performance.

In a heat sink 10 for radiating heat from an LED (heat source) 2 on the surface of a base plate 11 having multiple radiation fins 12 erected in parallel on the back, slits 11a (or holes) are formed in the base plate 11. Total area of the slits 11a (or holes) is set equal to (1/5-4/5) of the surface area of the base plate 11. Since convective effect by heat radiation is accelerated by an air flow passing through the slits 11a (or holes) of the base plate 11, in addition to heat radiation from the cooling fins 12 by heat transfer, heat radiation of the heat sink 10 is enhanced.