Rotation-speed sensor device

A rolling bearing unit with a rotation-speed sensor device for use in wheel support:

• the rolling bearing unit comprising a rotating race which rotates together with a wheel when moving,
• the rotation-speed sensor device comprising an encoder supported by a rotating race to be concentric with the rotating race and having a detected portion the characteristics of which are alternately changed in a circumferential direction,
• a rotation detection sensor supported by a non-rotating member and having a detecting portion facing the detected portion to produce a detection signal,
• a wireless transmission device for sending the detection signal from the rotation detection sensor to a controller provided on the vehicle chassis side, and
• a self-diagnosis circuit to judge whether there is a problem or not in detecting rotation-speed, and wherein the wireless transmission device has a transmission circuit which is kept with the rotation detection sensor in a single holder to form a sensor unit.