A parallel link mechanism with six degrees of freedom using electrohydraulic servo cylinders has large rigidity and support power. This feature is widely used for a driving device with multi degrees of freedom that has a heavy load or needs a large driving force. In this research, basic characteristics are revealed by experiment and theory. In the 1st report, the characteristics of the hydraulic servo system was considered, and a detailed mathematical model was made. A transfer function was obtained by linear approximation, and the frequency response was presented. In the 2nd report, nonlinear simulation was executed based on the detailed mathematical model. The frequency response obtained from the simulation agreed well with the experimental result. The appearance of fluctuation in each part was presented, and the influence of nonlinear characteristics was clarified. From this research, the dynamic characteristics between the input and output of one link that comprises a parallel link mechanism were clarified. However, the parallel link mechanism comprises a so-called interaction system where the displacement of one link influences those of other links through the end effector. In this report, the interaction that each link receives from one link is examined by experiment and nonlinear simulation. The appearance of interaction is presented when the input is a rectangular wave or sinusoidal wave. The frequency response of the interaction that each link receives is presented. It is clarified that the amplitude of the reference value for a link and the load mass has a large influence on the frequency response of interaction. It is also presented that Coulomb friction has a big influence on the result.