A detection signal representing changes of an object observed can be easily transmitted to any desirable site, without performing complex adjustment to use the signal. An AE sensor 21 is provided on an appropriate part of the circumferential surface of a rotating-side chuck 4 which holds a workpiece 5. A signal-transmitting unit 101 is provided in a space made in the rotating-side chuck 4. A signal-receiving unit 102 is mounted on an appropriate part of a main section 3 on which the rotating-side chuck 4 is provided. The signal-transmitting unit 101 transmits by radio a detection signal generated by the AE sensor 21. The signal-receiving unit 102 receives and demodulates the detection signal, generating a signal that will be processed in signal processing.