The invention relates to a device for detecting the rotation speed of a rotating element supported by at least one external rotating ring with at least one roller bearing. At least one internal non-rotating ring of the roller bearing is solidly connected to a shaft mounted on a support. The inventive device includes a non-rotating sensor adjacent to the roller bearing and a rotating encoder. The encoder is at least partially fixed by magnetization to a flange which is integral to the rotating ring and which is made from a magnetizable material.