In order to shorten the auxiliary times regarding tool and workpiece changing, conventional machine tools are equipped with automatic tool changers and automatic pallet changers, thus becoming machining centers. Reducing the time consumed with the change of the workpiece to follow in machining implies the existence of another table – i.e. the pallet – on which the workpiece is positioned and clamped, while on the working area of the machine another part is manufactured. This paper is presenting a new automatic pallet changer mechanism which is hydraulically driven, along with its guiding and transmission systems.