A generator is disclosed, in which connections among winding sets are changed to produce diverse powers different in voltage. A stator is composed of a stator core with teeth to form sequential slots, and many windings wound in the slots. The windings are grouped circumferentially in slot into winding sets, which are wound spaced circumferentially 120 electrical degrees apart to provide a three-phase system of windings. Any one winding set serves producing a low tension applied to automotive electrical system. A controller unit makes terminals of the windings in other winding sets connect in series and/or in parallel thereby producing powers different in voltage. As an alternative, the stator is comprised of an inside cylinder forming one surface of an air gap, a circular toothed member having teeth arranged circumferentially on the inside cylinder to form sequential slots opened radially outwardly of the stator, and an outside cylinder prepared separately from the toothed member then, followed by fit over the toothed member.