A rod-bed assembly has a holder with a groove into which an insert is removably and insertably supported. The apparatus has first and second rolling heads mounted at spaced positions along a common rolling arm to receive a crankshaft bearing therebetween which can then be shifted relative to one another along the common rolling arm to close the heads or rolling tools for clamping onto the workpiece. The circuit also outputs the current format amplified signals and a second gain control circuit connected after the first gain control circuit and having at least one gain control circuit which amplifies a current format amplified signal output from the first gain control circuit by a second gain.