A system for converting number of scanning lines converts a first number of scanning lines of a first digital video signal into a second number of scanning lines of a second digital video signal. The system comprises a discrete signal obtaining circuit supplied with the first digital video signal, for successively re-arranging a plurality of picture element information arranged along lines in a vertical direction with respect to a picture frame indicated by the first digital video signal within a time interval corresponding to the first number of scanning lines in units of each of the lines in the vertical direction in a time series manner, to obtain a discrete signal having a sampling frequency equal to a horizontal scanning frequency of the first digital video signal, a sampling frequency converter for converting the sampling frequency of the discrete signal obtained from the discrete signal obtaining circuit into a frequency equal to a horizontal scanning frequency of the second digital video signal, and a second video signal obtaining circuit for successively re-arranging an output of the sampling frequency converter in units of a plurality of picture element information along a direction of horizontal scanning lines in accordance with the second digital video signal in a time series manner, to obtain the second digital video signal using the second number of scanning lines.