A baffle plate assembly, configured to be coupled to a substrate holder in a plasma processing system, comprises a baffle plate having one or more openings to permit the passage of gas there through, wherein the coupling of the baffle plate to the substrate holder facilitates auto-centering of the baffle plate in the plasma processing system. A rear side of the module is not covered by the case. Since the interpolated signals are measurement targets, N-times oversampling measurement can also be performed for the discrete signals. The vibration reducing member is disposed on an opposite side of a rectilinear working axis of the tool bit from the rotating shaft and connected to a connecting part between the swinging member and the tool driving mechanism so as to be driven.