A rotation detecting device includes first and second magnetic detection elements that output first and second signals and a detection circuit having the first and second signals input thereto. The detection circuit includes an automatic correction circuit that performs generating and updating of a correction value for correcting the and second signals. The automatic correction circuit is configured to stop the generating or the updating of the correction value in at least one of a case where a rotation direction of an object is changed to a reverse rotation direction from a normal rotation direction and a case where a rotation direction of the object is changed to the normal rotation direction from the reverse rotation direction.