In a manufacturing system, the dynamic characteristics of a machine tool exert a profound influence on the machining accuracy of machine components. In particular, the performance of interface devices between machine tool and workpiece has significant effects on the machining accuracy and efficiency. Nevertheless, the characteristics of interface devises have not yet been sufficient research by the cause for their nonlinearity and complicated mechanisms. In this study, in order to improve the characteristics of a chucking system, the authors clarify and evaluate its dynamic characteristics. In particular, the relationship between the machining accuracy and the damping mechanism of a chucking system in a machine tool is investigated with a damper of electro rheological (ER) fluid. The results are as follows. (1) The damping characteristics of the ER damper in a chucking system of a machine tool can be controlled and improved by electric field intensity. (2) The damping characteristics are proportional to the yield stress of the ER effect. (3) The ER damper in the chucking system can improve machining accuracy in wide machining conditions. (4) An accurate evaluation method is proposed for damping characteristics.