A magnetic recorder and regenerator has a luminate signal input terminal for receiving a luminance signal, a line-sequential signal input terminal for receiving a line sequential signal consisting of alternately line-sequenced color differential signals having a d.c. level difference, and a detecting circuit for detecting the d.c. level difference in the line-sequential signal which is provided from the regenerator system of one magnetic recorder and regenerator used for signal regeneration and which is to be transferred, before being rearranged into its component color differential signals, to the recorder system of another magnetic recorder and regenerator used for signal recording. A gain-controlled amplifier is responsive to the output from the detecting circuit for adjusting the d.c. level difference in the line-sequential signal to a prescribed value, whereby it can suppress fluctuations in the line-sequential signal level during a dubbing process, avoiding picture quality deterioration. The magnetic recorder and regenerator also has a clamping circuit for clamping the d.c. level of the line-sequential signal and a color differential signal discriminating circuit for discriminating between the R-Y and B-Y components of the line-sequential signal in synchronism with a horizontal synchronizing signal, and for providing a clamp timing signal to the clamping circuit to clamp the line-sequential signal corresponding to either one of the R-Y and B-Y components.