PURPOSE:To fetch an object signal quickly by deviating a gate signal generating point increasingly and decreasingly in the unit of one line around a generating point of a gate signal generated at first when a fetched signal is not an object signal so as to generate a gate signal of a line for the object signal. CONSTITUTION:When a fetch discrimination circuit 3 discriminates it that a fetched signal is not an object signal, since an error signal NG is inverted to a high level, a frame pulse FD is used as an output signal NGCLK of an AND gate 14 and it is fed to a clock terminal CLOCK of a quinary counter 15. Then the gate signal generating point is deviated increasingly and decreasingly sequentially in the unit of one line around the position of a gate signal generated at first by means of a selector 13 to generate a gate signal by which the object specific signal is able to be extracted. Thus, the object signal is fetched in a short period of time.
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