A rotor of a vehicle AC generator is comprised of a rotor core and a field coil. The rotor core is comprised of a boss portion and a plurality of claw-pole portions bending to respectively extend in axial directions from outer circumferences of the boss portion to interleave with each other to form a zigzag space between the claw-pole portions. The field coil comprises a main coil portion disposed on the boss portion, a sub-coil portion disposed between the main coil and the claw-pole portions and a flywheel diode connected in parallel with the main coil. When the field current is cut off, current circulating through the main coil is increased because the energy accumulated in the sub-coil is discharged.