PURPOSE: To provide a synchronizing mechanism excellent in responsiveness while absorbing an extension/contraction error between cylinders.

CONSTITUTION: An extension/contraction guide post 5 for guiding vertical motion of a shaking table 3 and a plurality of heave cylinders 8 arranged parallelly to this guide post 5 to vertically move the shaking table 3 are provided, and control valves 13 for controlling a flow of supply actuating fluid relating to the heave cylinders 8 are respectively provided in the vicinity of each heave cylinder 8, further it is connected to the guide post 5 through a synchronizing link 10.