1. A video signal processing apparatus, comprising: a first correlation detecting unit obtaining a correlation value of every symmetric pair of pixels positioned in a point-symmetry, center of which is an interpolation pixel on an interpolation line interpolated between two real lines, the symmetric pair of pixels being positioned on the two real lines of an input video signal respectively; a second correlation detecting unit obtaining a correlation value of every pair of pixels for the symmetric pair of pixels and one or more parallel pairs of pixels positioned in a direction which is parallel to a direction of the symmetric pair of pixels, the parallel pair of pixels being positioned on the two real lines of the input video signal respectively; a correlation direction deciding unit deciding any one of a correlation direction based on the correlation value from the first correlation detecting unit and a correlation direction based on the correlation value from the second correlation detecting unit as a correlation direction which is a direction of a pair of pixels used for generating the interpolation pixel; and an interpolation pixel generating unit generating a pixel signal of the interpolation pixel by using the pair of pixels based on a decision result of the correlation direction deciding unit.