A vehicle A.C. generator has a rotor. The rotor has a pair of pole cores and magnet holders. Each pole core has a plurality of claw-like magnet poles. Each magnet holder contains a permanent magnet and placed between the adjacent claw-like magnet poles in order to prevent leakage flux. The rotor has a pair of supporting members in order to stop each magnet holder shifting in the direction of a rotary shaft of the rotor. Each supporting member has projecting parts which correspond to the magnet holders. The supporting members are fixed to one end surface of the pole cores, respectively. Each projecting part fixes the position of the corresponding permanent magnet in the rotor.