A rotor for an automotive alternator comprises a cylindrical bobbin fitted over the base portions of a pair of field cores having a cylindrical portion, a pair of first and second annular flange portions projecting perpendicularly from both ends of the cylindrical portion, a recessed groove disposed at an angle to the radial direction in the inner wall of the first flange portion, and an anchor portion disposed on an outer circumferential portion of the first flange portion in close proximity to the outer circumferential end of the recessed groove; and a field winding having a circular cross-section, the starting portion of which is wound around the anchor portion and housed in the recessed groove, then drawn from the inner circumferential end of the recessed groove onto the outer circumferential surface of the cylindrical portion of the bobbin, and additionally wound a predetermined number of turns into multiple layers on the cylindrical portion of the bobbin, at least one portion of the field winding excluding the prewind portion and the postwind portion being formed with a rectangular cross-section.