An alternator of high quality and high performance includes a rotor, a stator core arranged so as to surround the rotor and having a plurality of axially extending slots arranged at a predetermined circumferential pitch, and a stator having a stator winding fitted into the slots. The stator core includes element iron cores of a hexahedral shape which are deformed to curve, with their adjacent end faces being abutted and bonded to each other, each of the element iron cores being composed of thin steel plates laminated and integrated with one another, with concave and convex portions formed on the thin steel plates being fitting with each other. The concave and convex portions are formed on a borderline between a compressive region of the stator core at an inner diameter side thereof and a tensile region of the stator core at an outer diameter side thereof.