For a vehicle fatigue and strength testing system, two methods are usually used to accurately simulate the road-load on the test bench: one is the “separation of road-load into multi-axial loads” method and the other is the “compensation with frequency response function” method.These methods have remarkably improved the abnormality detection capability and accuracy of bench testing.For power steering or other units, however, the road-load points drift while the vehicle is driven. Further more, the road-load is applied in a complex manner to the vehicle. These factors make it difficult to separate the road-load into multi-axial loads and to provide stable measurement of the frequency response function. Thus, further progress of these methods has been delayed.The objective of this study was to make the bench testing of power steering units possible. To separate the road-load into multi-axial loads, we located the loading unit pivots hyperbolically and devised a twin parallel link mechanism. In addition, we introduced a coherence function to smooth and stably measure the frequency response function.As a result, we made it possible to dynamically evaluate power steering units in five axial directions on a test bench. We could detect knocking noise and other abnormalities more reliably, and improved the reproducibility of road-load produced during actual operation of vehicle.