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 is provided on an appropriate part of the circumferential surface of a rotating-side chuck which holds a workpiece. A signal-transmitting unit is provided in a space made in the rotating-side chuck. A signal-receiving unit is mounted on an appropriate part of a main section on which the rotating-side chuck is provided. The signal-transmitting unit transmits by radio a detection signal generated by the AE sensor. The signal-receiving unit receives and demodulates the detection signal, generating a signal that will be processed in signal processing.