A heatsink including: a heat transport member having a heat receiving portion thermally connected to a heating element; and a heat radiating fin group which is connected to a heat radiating portion of the heat transport member and in which a plurality of heat radiating fins is arranged, wherein the heat transport member has an integral internal space that communicates from the heat receiving portion to the heat radiating portion and that is filled with a working fluid, a heat receiving portion inner surface area increasing portion and a supporting member are provided in an internal space of the heat receiving portion, and the supporting member is in surface contact with the heat receiving portion inner surface area increasing portion.