A faster and more streamlined system for providing summary and analysis of large amounts of communication data is described. With the aid of a control unit, control signals are generated from the signal of the far-end subscriber, the output signal of the loudspeaker-room-microphone system and the output signal of an adaptive filter used as reference, the control signals having an amplitude and a time response dependent on the speech mode. The engagement device includes a differential pressure generating chamber that receives oil supply so as to apply hydraulic pressure to a side of the pressing member opposite to a side to which hydraulic pressure for operation is applied.