A vehicle alternator has a rotor having plural claw poles and a stator placed at the outer circumference of the surface of the rotor. Plural grooves are formed in a specified rear area on a surface of each claw pole faced to the stator. The specified rear area is an approximate rear half area on the surface of the claw pole along a rotating direction of the rotor. The grooves are formed in parallel to each other. Each groove has one or a combination of a U-letter shaped groove having a circulation-arc shaped bottom, a rectangle shaped groove having a rectangle shaped bottom, and the like. The configuration of each claw pole ensures the reduction of generating an eddy current on the surface of each claw pole and thereby prevents a reduction of output power of the vehicle alternator.
