An abnormality detecting device and method for detecting a symptom of a failure of a spindle of a machine tool before the spindle malfunctions. The abnormality detecting device for detecting an abnormality or malfunction includes a spindle motor and a motor controller. The motor controller includes a time measuring part which measures a spindle stopping time from when a free-run of the spindle motor accelerated to a predetermined number of rotations is started to when the spindle motor is stopped, a storing part which stores the spindle stopping time measured by the time measuring part, and a comparing part which compares a plurality of data with respect to the spindle stopping time stored in the storing part, and judges as to whether or not an abnormality exists in the spindle or the spindle motor.