Correlation of videos between fields is determined between a difference between an input interlaced signal and a signal that is delayed by one field with respect to the input interlaced signal. Correlation among N-1 sequential fields is compared with a predetermined pattern to determine whether the input interlaced signal is unquestionably a telecine-converted signal, whether it is unquestionably not a telecine-converted signal, or whether it cannot be said to be unquestionably a telecine-converted signal. If a determination of being unquestionably a telecine-converted signal is continued for a predetermined number or more of fields, an instruction signal, which instructs to perform inter-field interpolation on the input interlaced signal, is outputted.