Abstract: When an A/D-converted composite video signal is directly outputted while a system clock frequency is switched so as to execute the determination of a signal system, a digital chroma demodulation system prevents the images displayed by the composite video signals from distorting in accordance with switching of frequency of system clock. As for a frequency m (=fsc×n) of system clock synchronizing with a color burst signal, a frequency m of system clock between systems is set to fall in a predetermined range by changing a coefficient n in accordance with a system (a color bust signal frequency). Thus, since a composite video signal is A/D-converted in accordance with a substantially constant sampling frequency, the sampling condition such as a sampling frequency and a sampling point is not greatly changed.