An interpolation interval Vdp obtained by the picture sizes of the original picture and the converted picture is cumulated by an adder. In the odd field, a selector selects [0.5] as an offset corresponding to an odd/even field determination signal. In the even field, the selector selects [0] as an offset corresponding to the odd/even field determination signal. In a vertical blanking interval, the offset is selected as an output. Thus, in the odd field, the offset value [0.5] is added to the cumulated value of Vdp. Thereafter, Vdp is cumulated again. Corresponding to the cumulated value, a line read address n and linear interpolating coefficients qn1 and qn2 are obtained. When Vdp is cumulated, offsets corresponding to the scanning start points in the odd field and the even field are added. Thus, the interlace accuracy is kept.