To provide a rotation detection sensor that is fixed to a sensor fixation member by a simple fixation structure so that a sensor unit is positioned, and has improved waterproofness and vibration resistance.

The rotation detection sensor is fixed to the sensor fixation member 7 mounted to a bearing for wheels and detects rotation of a rotary ring in the bearing for wheels. A sensor unit B includes: a magnetic sensor element 1 for detecting a body to be detected in the rotary ring; a cable 10 for taking out the output signal to the outside; and a substrate 11 to which one end of the sensor element 1 and one end of the cable 10 are mounted while having a conductive section 3 for connecting an electrode section 2 of the sensor element 1 and a conductor 4 of the cable 10. Recesses 11a or projections at least at one place or more provided on the substrate 11 are fitted to projections 7d or recesses provided in the sensor fixation member 7, thus fixing the sensor unit B to the sensor fixation member 7. By covering the sensor unit B, a molding section 8 obtained by forming a molding material made of thermoplastic elastomer or a rubber material is provided.