PURPOSE: To prevent malfunction, by outputting a pulse signal with inverting and non-inverting so as to attain stable signal discrimination, in response to a phase difference between a pulse signal obtained from a horizontal synchronizing signal having flywheel effect and a detection specified signal.

CONSTITUTION: If an erroneous pulse is generated in an output signal S5 of an AND circuit 22, a capacitor 36b repeats charge/discharge in response to the combination of levels of the erroneous pulse and a signal S6 and a potential VC of the capacitor 36b of an LPF 36 is changed. But the holding effect of the LPF 36 is strong, an output signal at an output terminal 40, i.e., a line sequential signal S7 of a blue color differential signal B-Y and a red color difference signal R-Y is not inverted and the stable detection of the blue and the red color difference signal is attained.