PURPOSE: To prevent vertical vibration from being transmitted outside, by providing counter weights which vibrate respectively in the vertical and rotating directions in the opposite phases.

CONSTITUTION: When an electromagnet 15 is applied with alternate current, a rotary neutral plate 11 is alternatively attracted and vibrated vertically. Another vertically vibrating system consisting of a lower plate 17 and a leaf spring 13b is subject to the reaction of the vertically vibrating system 13a and vibrate in the opposite phase to the system 13a. By adjusting the leaf springs 13a and 13b and the corresponding portions of the mass so as to equalize the natural frequencies of these vertically vibrating systems 13a and 13b, any vertical vibration transmitted to the base 12 is offset to prevent it from vibrating vertically, and thus the vibration can be effectively prevented from being transmitted outside.