An object of the present invention is to provide an automotive alternator achieving high output by overlapping a laminated core of a stator and yoke portion of a field rotor in an axial direction, and enabling electromagnetic noise to be reduced by prescribing dimensional relationships in the field rotor. In this automotive alternator, a ratio (R2/R1) between an outer radius R2 of a cylindrical portion of a Lundell-type core and an outer radius R1 of the Lundell-type core is set to a range from 0.50 to 0.54, and a ratio (Tr/Tp) between an axial overlap length Tr between the laminated core of the stator and the yoke portions of the Lundell-type core and an axial length Tp of the yoke portions is set to a range greater than or equal to 0.2.