A circuit board heatsink 60 for cooling a regulator circuit board has a flat base portion 61. Fifteen fins 62 are respectively disposed so as to project vertically from a first surface of the base portion and are arranged so as to be parallel to each other. The regulator circuit board is fixed to a second surface of the base portion 61 of the circuit board heatsink 60, and is housed and held inside a regulator circuit board housing portion of a regulator assembly such that the fins 62 face the rear bracket.