A heat sink according to the present invention includes a heat receiving member which receives heat of heat generating components, a plurality of heat radiation fins arranged on the heat receiving member; and a cover member, which covers the plurality of heat radiation fins. Flow passages in which a fluid flows are formed between the adjacent heat radiation fins. The cover member is provided on the heat receiving member and opens both ends of the flow passages. The cover member is provided with at least one hole through which a fluid outside of the cover member is introduced into the fluid flowing in the flow passages.