The present disclosure provides a heatsink that can improve heat radiation efficiency of a heat radiating fin and equalize a heat input in a heat receiving portion while securing sufficient volumes of the heat receiving portion, a heat insulating portion, and a heat radiating portion even in an environment in which an installation space for the heatsink, more specifically, an installation space in a width direction of the heatsink is limited.
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 thermally 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, and a cross-sectional area of an internal space in a direction orthogonal to a heat transport direction of the heat transport member in the heat radiating portion is larger than the cross-sectional area in a heat insulating portion between the heat receiving portion and the heat radiating portion.