Résumé dans la langue de publication Objects of the present invention are to provide a highly mass-producible heat sink ensuring excellent cooling performance, and to provide an automotive alternator capable of stable running by suppressing temperature increases in diodes of a rectifier and in a stator. The heat sink is a die cast provided with a flat base 41 having a generally rectangular planar shape, one surface thereof constituting a surface for mounting heat-generating components, and a plurality of fins 42 disposed on the other surface of the base 41 at a pitch (P) in the longitudinal direction of the base, each rising perpendicularly from the other surface of the base and projecting in the longitudinal direction of the base, the projecting height (H) of the fins from the base being five or more times the thickness (T) of the fins. The plurality of fins 42 are formed such that the thickness (T), height (H), and pitch (P) of the fins satisfy the expressions T <= 1 mm and 0.35 <= T <= 0.6.