A coolant passageway (2) of a heat sink (1) has a coolant lead-in part (21), a coolant lead-out part (22), coolant-contact parts (23), coolant-transit parts (25), and connecting parts (24). The coolant-contact parts (23) are disposed spaced apart from one another along a coolant path leading from the coolant lead-in part (21) to the coolant lead-out part (22) and are configured such that they bring the coolant into contact with a cooling-wall part. The coolant-transit parts (25) are disposed between adjacent coolant-contact parts (23) and are configured such that the coolant can transit from upstream-side coolant-contact parts (23) to downstream-side coolant-contact parts (23) in the coolant paths. The connecting parts (24) are interposed between the coolant-transit parts (25) and the coolant-contact parts (23) and have a passageway cross-sectional area that is smaller than those of the coolant-contact parts (23) and the coolant-transit parts (25).