Abstract: Encoder device for a rotational speed sensor of a rotating member of the bearing (1) mounted on a non-rotating member of the said bearing (1), of the type comprising a sensor (7) which is secured to an element that is fixed relative to the non-rotating member and in front of which an element forming a rotor moves in rotation with a small air gap, which element is equipped with an encoder (12) in the form of a multipole magnetized ring, capable of producing in the sensor a periodic signal of frequency proportional to the speed of rotation of the rotor element. The encoder (12) is fixed to an internal face of a rigid protection and support element (13) made of nonmagnetic metallic material, a corresponding external face of the protection element (13) moving in rotation in front of the sensor (7).