In a voltage adjuster for a vehicle AC generator which has a cooing member for cooling a circuit portion of the voltage adjuster and in which plural fins of the cooling member are disposed so as to face an air suction hole formed in a case, the cooling member is constructed by assembling a first cooling plate having the same cross-sectional surface in a generating and processing direction and at least a second cooling plate having the same cross-sectional surface in a generating and processing direction and the same cross-sectional surface shape as the first cooling plate, and the fin end surfaces of one cooling plate are abutted on the other cooling plate so as to face the ventilation paths formed by the plural fins of the other cooling plate.