PURPOSE: To easily vary or adjust the characteristic frequency of a main mass by elastically supporting the main mass on a supporting frame through a nonlinear coil spring, and varying the spring constant of a nonlinear coil spring by adjusting a preset deflection adjusting bolt installed on a supporting frame.

CONSTITUTION: As for a vibration suppressing device 30, a main mass 20 is elastically held on a supporting frame 10 through coil springs 25 and 27 which possess the nonlinear load/deflection characteristic, and each spring constant of these springs 25 and 27 is the sum of the spring constant of the coil springs 25 and 27. Accordingly, the spring constant of each coil spring 25, 27 is varied by screwing or screwing back a preset deflection adjusting bolt 29 for the upper plate 101 of the supporting frame 10, and the spring constant of the whole can be varied, and the characteristic frequency of the main mass 20 can be adjusted easily.