A frame rate conversion, for instance between NTSC and PAL, or SECAM, has been improved by interpolation system in which an interpolation is performed from picture elements of two consecutive frames of an original picture signal whose positions are shifted from the position of a picture element to be interpolated by amounts related to the move length of a picture block between the two consecutive frames period, instead of using picture elements of two consecutive frames of the original signal that have the same position coordinates as those of the picture element to be interpolated. Picture quality of the converted signal is improved in particular when a picture moves.