PURPOSE: To impart a clean sinusoidal acceleration to a sample by performing feedback control through a hydraulic cylinder for absorbing impact interposed between a coupling of a driving hydraulic cylinder and a table thereby absorbing distortion of acceleration caused by frictional force of the cylinder, backlash of the coupling, or the like.

CONSTITUTION: When a table 7 is vibrated through motion of a piston 3 in a driving cylinder 11, the driving force Fc functions on a filtering hydraulic cylinder 14 as an external force thus urging the cylinder 14 to shift from a neutral position. But since the opposite ports of the cylinder 14 are short- circuited through an orifice 18 to constitute a positional servo system, shift X from the neutral position decreases as the value Ka of gain 21 increases in the servo system. Consequently, spring constant Kf of the cylinder 14 can be controlled through control of the gain Ka. Distortion in the acceleration of the table 7 caused by backlash of the coupling or the like may exceeds three times of shaking frequency, but it causes no distortion in the acceleration of the table 7 so long as the distortion occurs in the lowering region of gain.