A wheel speed sensor capable of stabilizing a projecting posture of a sensor unit when attached to a vehicle is provided. The wheel speed sensor includes a mounting base providing a first contacting part and a second contacting part when attached to the vehicle to come into contact with the vehicle at two positions of the first contacting part and the second contacting part, the sensor unit projecting from a position between the first contacting part and the second contacting part and inclining toward the first contacting part, the sensor unit being resin molded integrally with the mounting base and including a signal detection device provided in a distal end of the sensor unit, and a fixing member pressing and fixing the mounting base to the vehicle at a position between the first contacting part and the sensor unit.