A condition detection apparatus comprising an AE sensor 1 that detects AE waves, which elastically-occur when a plurality of balls included in an LM system self-rotate and revolve within a circulation section at the same time, and generates detection signals Sae, and a signal processing unit 4 that generates a first parameter indicating an intensity of the AE waves based on the generated detection signals Sae, generates based on the detection signals Sae a second parameter by weighting only detection signals Sae temporally-continuously detected among the detection signals Sae, generates based on the detection signals Sae a third parameter by weighting only detection signals Sae temporally-discontinuously detected in correspondence with the movement of the balls among the detection signals Sae, and judges contents of an operational condition of the LM system using any one of the first, second or third parameter, is provided to enable prognosis of occurrences of failures in the LM system, to improve maintainability for a user of the LM system, and to contribute to the prolonging of the operation life of the LM system as well as performance assurance and quality improvement of apparatuses or devices incorporated with the LM system.