A signal processing device for processing an information signal is arranged to detect a signal included in the information signal and appearing during each given blanking period of the information signal in which a plurality of kinds of signals appear in sequence at intervals of the blanking period and the DC level of the information signal is offset according to the kind of a signal appearing during each of the blanking periods, to remove the DC level offset of each blanking period of the information signal by using the signal thus detected, and to identify the kind of signal included in the information signal by using the signal detected. The arrangement facilitates a reduction in size and weight of the device by reducing the number of external elements and the number of external-element connecting terminals.