PURPOSE:To detect the relative plane position and to prevent the output of a compensating signal when the centering has coincidence, by processing the 1st, 2nd and 3rd output video signals supplied from an image pickup tube through a processing circuit containing a 1H delay circuit, an adder circuit, etc. CONSTITUTION:The green video signal SAG supplied to a terminal 11G of a horizontal centering detecting circuit used to a multi-tube type image pickup device is delayed by a horizontal period through a delay circuit 31 and applied to a synthesizer 32. At the same time, red and blue video signals SAR and SAB from terminals 11R and 11B selected by a switch 15 are added with each other. Then a difference signal SE between signals SRA and SAG is outputted. The signal SE is delayed through a delay circuit 33, and this delayed signal is added with the signal SE. Then a difference signal SG is applied to a comparator 35 to be compared with a difference signal SC outputted from the synthesizer 32. The result of this comparison is applied to a sample holding circuit 37. The output of the circuit 37 is controlled with the output of a rectifying circuit 20 which supplies the signal SC. Thus no compensating signal is outputted when the centering has coincidence.
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