ROTATION DETECTING DEVICE AND BEARING EQUIPPED WITH ROTATION DETECTING DEVICE

A rotation detecting device provided in a bearing assembly comprising: an annular encoder provided rotatably and having a plurality of to-be-detected poles circumferentially equidistantly arranged therein; a sensor for detecting the to-be-detected poles of the encoder; a multiplying unit for multiplying a phase of the to-be-detected poles based on an output of the sensor; a pulse outputting unit adapted to receive an output of the multiplying unit or both an output of the multiplying unit and a detection output of the sensor and capable of outputting pulses of at least two types of magnifying powers that are different from each other; and a cap that covers an end face opening of an outer member of the bearing assembly. The device may output either ordinary pulses without passing them through the multiplying unit, or high resolution pulses after passing them through the multiplying unit. The cap comprises a cylindrical metal member having a plurality of slits, to form a series of separate mounting tabs.