An apparatus and method for interpolating lines of input image signal. The apparatus has a detection unit for detecting a directional characteristic and an angle with respect to a horizontal direction of a sampled edge component obtained by sampling the edge component of an upper horizontal line and a lower horizontal line in an area around a pixel to be interpolated; a judgment unit for judging whether an error is generated based on the directional characteristic and the angle detected by the detection unit and an average value of pixels corresponding to the directional characteristic and the angle; and an image signal generation unit for generating a line interpolated image signal by line interpolating an input image signal, according to a result judged by the judgment unit.