To acquire a high-resolution frame from a plurality of frames sampled from a video image, it is necessary to obtain a high-resolution frame with reduced picture quality degradation regardless of motion of a subject included in the frame. Because of this, between a plurality of contiguous frames Fr.sub.N and Fr.sub.N+1, there is estimated a correspondent relationship. Based on the correspondent relationship, the frames Fr.sub.N+1 and Fr.sub.N are interposed to obtain first and second interpolated frames Fr.sub.H1 and Fr.sub.H2. Based on the correspondent relationship, the coordinates of the frame Fr.sub.N+1 are transformed, and from a correlation value with the frame Fr.sub.N, there is obtained a weighting coefficient .alpha.(x.degree., y.degree.) that makes the weight of the first interpolated frame Fr.sub.H1 greater as a correlation becomes greater. With the weighting coefficient, the first and second interpolated frames are weighted and added to acquire a synthesized frame Fr.sub.G.