In an alternator of this invention, a ratio (t1/t2) between a radial thickness (t1) of a tip and a radial thickness (t2) of a root portion is within a range equal to or greater than 0.10 and equal to or less than 0.25, with a ratio (A/B) between a dimension (A) of overlap between a stator core and disk portions when viewed from a radial direction and an axial dimension (B) of the disk portions being within a range equal to or greater than 0.2 and equal to or less than 1.0, and a ratio (Lp/Lc) between an axial length (Lp) of claw-shaped magnetic poles overlapping the stator core when viewed from a radial direction and an axial length (Lc) of the stator core being within a range equal to or greater than 0.7 and equal to or less than 0.9.