PURPOSE: To suppress ripple components of a signal voltage and to reduce the influence upon a control system by inputting a magnet position detection signal to logical processing circuits and rectifying an AC voltage across stator winding synchronously in full-wave basis by using the output signals of the logical processing circuits.

CONSTITUTION: A brushless tachometer generator is constituted by arranging the stator winding and magnet position detectors HAWHC opposite a magnet rotor and magnetic pole position signals AWC obtained by the magnet position detectors HAWHC are inputted to the logical circuits respectively to generate doubled select signals D1WF2. Those select signals are used to rectify the AC voltage across the stator winding synchronously on full-wave basis, obtaining a DC voltage corresponding to the rotating speed of the rotor. Consequently, ripples of the DC voltage are reduced as compared with half-wave rectification in which the signals AWC are used as they are, and the whole control system in which the generator is incorporated is stabilized.