A vehicle alternator is constructed such that satisfies the relationship0.3.ltoreq.{Br.multidot.(t1+t2).multidot.L}/(W.multidot.t1.multidot.cos.theta.).ltoreq.2.0where Br represents the residual magnetic flux density of each of the magnets, L represents the length from the short side at the tip to the long side at the base of each of the claw-shaped magnetic poles, W represents the width in the circumferential direction at the base, 2.theta. represents the angle formed by an oblique side which joins one end of the tip to one end of the base and another oblique side which joins the other end of the tip to the other end of the base, t1 represents the thickness of each of the claw-shaped magnetic poles at the base, and t2 represents the thickness of each of the claw-shaped magnetic poles at the tip.