An image processing apparatus for reducing a load of processing of an interpolation operation at the time of a correction of keystone distorted image is provided. The image processing apparatus has an interpolating means (11, 12) for receiving as input original image data, executing a first interpolation operation a plurality of times with respect to a plurality of original pixel data arranged in one direction of a vertical direction or a horizontal direction in the original image data, executing a second interpolation operation in the other direction, and generating new image data and a storing means (13) for storing the interpolated data (Va to Vd) obtained by the first interpolation operations, wherein, where a combination of a plurality of original pixel data is the same as a combination used when the interpolated data (Va= to Vd=) already stored in the storing means (13) were calculated, the interpolating means (12) reads out that interpolated data from the storing means (13) and uses the same for the second interpolation operation.