correlation with a sampling point in the n 2 field and the sampling point l has correlation with the principal sampling point in the n field the comparator 260 judges that the principal sampling point in the n field has correlation with the sampling point f in the n 1 field and corrects the result of detection of correlation of the principal sampling point a correlation detecting signal at the point n which is output one frame and four pixels behind the correlation detecting signal 114 and a correlation detecting signal at the point g which is output one line behind the correlation detecting signal 114 are input to the comparator 261 if the direction of correlation of the sampling point g is right hand downward in fig1 b and the sampling point g has correlation with a sampling point in the n 2 field and the sampling point n has correlation with the principal sampling point in the n field the comparator 261 judges that the principal sampling point in the n field has correlation with the sampling point g in the n 1 field and corrects the result of detection of correlation of the principal sampling point a correlation detecting signal at the point m which is output one frame one line and two pixels behind the correlation detecting signal 114 and a correlation detecting signal at the point e which is output two pixels behind the correlation detecting signal 114 are input to the comparator 262 if the direction of correlation of the sampling point e is right above in fig1 b and the sampling point e has correlation with a sampling point in the n 2 field and the sampling point m has correlation with the principal sampling point in the n field the.