To provide a heat sink capable of enhancing heat dissipation performance.Cylindrical bodies 3 have openings 3a of which inner and outer sides are opened on front ends and are provided with through-holes 3b communicating the inner side and the outer side on side walls at the base end side. The cylindrical bodies 3 are provided in a standing manner in a state where portions at the base end side penetrate through a supporting main body 2 and project into a gap s1, the through-holes 3b are opened to the gap s1, and portions at the front end side also project from the surface of the supporting main body 2 at the opposite side to the gap s1. An atmosphere in the gap s1, which contains heat from a cooling target object 9, is capable of being made to flow into the cylindrical bodies 3 through the through-holes 3, circulate in inner spaces of the cylindrical bodies 3, and be released to the outside through the openings 3a on the front ends.