A heatsink includes: a base plate thermally connected to a heat-generating unit; a plurality of heat radiation fins erected on a surface of the base plate, and arranged with gaps in a first direction along the surface; and a partition member provided to intersect the plurality of heat radiation fins, and partitioning the plurality of heat radiation fins in a second direction along the surface and intersecting the first direction. The partition member partitions the plurality of heat radiation fins such that more air passes through in the second direction between the plurality of heat radiation fins on a base plate side than on a side opposite to the base plate side.