A heat sink , comprising: a plurality of heat pipes ; and radiation fin parts respectively corresponding to the plurality of heat pipes , the radiation fin parts being fixed to respective end parts of the plurality of heat pipes in a longitudinal direction, wherein each radiation fin part of the radiation fin parts is composed of a plurality of fin plates and a gap is formed between adjacent fin plates of the plurality of fin plates belonging to different radiation fin parts, each fin plate of the plurality of fin plates has a fixing part for thermal connection to the corresponding heat pipe of the plurality of heat pipes , at least one heat pipe of the plurality of heat pipes is fixed to each fin plate of the plurality of fin plates , a fin plate assembly is constituted of the plurality of fin plates of the plurality of respective radiation fin parts as seen from a direction in which the corresponding heat pipe of the plurality of heat pipes extends, the plurality of heat pipes are composed of a first heat pipe group and a second heat pipe group , each heat pipe and corresponding radiation fin part of the first heat pipe group are disposed to line up with each other and each heat pipe and corresponding radiation fin part of the second heat pipe group are disposed to line up with each other, a first fin plate of the plurality of fin plates that is thermally connected to the first heat pipe group includes an expanding part , and characterized in that the first fin plate is configured such that a first area , at a periphery of the fixing part , is smaller than a second area , occupied by the expanding part of the first fin plate , which increases a radiation area close to the corresponding heat pipe . a plurality of heat pipes ; and radiation fin parts respectively corresponding to the plurality of heat pipes , the radiation fin parts being fixed to respective end parts of the plurality of heat pipes in a longitudinal direction, wherein each radiation fin part of the radiation fin parts is composed of a plurality of fin plates and a gap is formed between adjacent fin plates of the plurality of fin plates belonging to different radiation fin parts, each fin plate of the plurality of fin plates has a fixing part for thermal connection to the corresponding heat pipe of the plurality of heat pipes , at least one heat pipe of the plurality of heat pipes is fixed to each fin plate of the plurality of fin plates , a fin plate assembly is constituted of the plurality of fin plates of the plurality of respective radiation fin parts as seen from a direction in which the corresponding heat pipe of the plurality of heat pipes extends, the plurality of heat pipes are composed of a first heat pipe group and a second heat pipe group , each heat pipe and corresponding radiation fin part of the first heat pipe group are disposed to line up with each other and each heat pipe and corresponding radiation fin part of the second heat pipe group are disposed to line up with each other, a first fin plate of the plurality of fin plates that is thermally connected to the first heat pipe group includes an expanding part , and characterized in that the first fin plate is configured such that a first area , at a periphery of the fixing part , is smaller than a second area , occupied by the expanding part of the first fin plate , which increases a radiation area close to the corresponding heat pipe . <EOS>