To provide a rotation detection sensor capable of detecting the abnormality of a sensor by the sensor itself, to be output, without depending on a rotation speed of a rotor.

This rotation detection sensor includes two rotation detecting parts 1 for outputting respectively pulse-like rotation detection signals S1, S2 in response to the rotation of the rotor 30, a rotational direction detecting part 4 for detecting a rotational direction of the rotor 30, based on the two-phase rotation detection signals S1, S2 output respectively from the rotation detecting parts 1, an abnormality detecting part 6 for detecting the abnormality of the rotation detecting parts 1, and a signal processing part 8 for generating the pulse-like first output signal and second output signal indicating the rotational direction and the rotation speed of the rotor 30, to be output, when the rotation detecting parts 1 are normal, and for generating the third output signal having a pulse shape different from those of the first output signal and the second output signal, and indicating an abnormal state and the rotation speed of the rotor 30, to be output, when one of the rotation detecting parts 1 is abnormal.