state as the outer check ring 320 having a smaller rigidity than a wall surface of the hydraulic chamber 384 is deformed the fluid is pushed out of the hydraulic chamber 384 of the hydraulic power unit 300 a through the fluid outlet 383 the first driving signal of the driving module is also applied to the oscillator 350 of a neighboring hydraulic driving unit for example 300 b as the signal is applied the oscillator 350 and the vibration tube 375 are deformed such that the pressure in the hydraulic chamber 384 is reduced backward direction when the pressure in the hydraulic chamber 384 is reduced the outer check ring 320 is maintained in a state being adhered to the fluid outlet 383 and the inner check ring 340 does not seal the fluid inlet 381 and thus a fluid may be pressurized into the hydraulic chamber 384 of the hydraulic driving unit 300 b via the fluid inlet 381 at which the inner check ring 340 is disposed when all of hydraulic power units and elements connected to inner and outer portions thereof are filled with a fluid and sealed the fluid inside the sealed space may be circulated in a desired direction to thereby prevent cavitations in the fluid in order to.