To automatically suppress vibration caused by an excavating part by providing a damping device, put in damping action by an antiphase signal, at an excavating part or a lower part of a bucket elevator.

During operation, vibration is detected by a vibration detecting device 1, and vibration waveform is passed through a filter 2 to take out vibration waveform of object frequency. The filter 2 can be so formed as to have several kinds of frequency pass bands, and the vibration waveform of its maximum level can be used. An antiphase signal generating part 3-1 has a predetermined reference level, starts action when the level of the vibration waveform from the filter 2 exceeds this reference level and outputs an antiphase signal with an antiphase to the vibration waveform. A phase fine adjustment part 3-3 monitors the vibration value from a vibration value detecting part 3-2 and outputs the antiphase signal. A damping device 4 is vibrated by this antiphase signal and acts in such a way as to nullify vibration caused by an excavating part.