The rotary
detector according to this invention comprises a rotary
detector unit C1, C1′ which detects rotary motion of a rotor; and a rotary
calculator unit C2, C2′, C2″ comprising a rotation angle
detector, which detects the rotation angle of the rotor, and an angle speed detector 47 which detects the angle speed of the rotor, based on the output of the rotary detector unit. The rotary
calculator unit comprises a trigonometrical
calculator C3, C3′, C3″ which calculates a sine value or a cosine value of the rotation angle detected by the rotary detector; a
gain adjuster 57, 57′, 57″ which multiplies the sine value or the cosine value, calculated by the trigonometrical calculator, by a predetermined
gain; a multiplier 59, 59′ which multiplies the output of the
gain adjuster by the output of the angle speed detector; and a subtracter 61, 61′ which subtracts the output of the multiplier from the output of the angle speed detector.