PURPOSE: To enhance a measuring accuracy of an unbalance by a method wherein a natural frequency in a vibration system of a vibration table is extremely easily adjusted in a short time.

CONSTITUTION: The title table consists of brackets 2A, 2B of upper and lower sections, horizontal rod spring bodies 4A, 4B of the upper and lower sections horizontally and respectively projected in front and rear directions (y) from the brackets 2A, 2B, a vertical rod spring body 6 provided on a floor face 5 of a supporting table, a vibration body 7 which is supported by both of the rod spring bodies 4A, 4B, 6 and holds a rotor and a vibration detectors 9A, 9B that detects, via a connection member 8, the vibration of the vibration body 7 in right and left directions (x) perpendicular to a projection direction of the horizontal rod spring bodies 4A, 4B. Supporting positions of the horizontal rod spring bodies 4A, 4B by the brackets 2A, 2B in the front and rear directions are adjustable.