This invention provides an image processing apparatus for executing padding processing at a high speed. For this purpose, the image processing apparatus of this invention is an image processing apparatus for processing image data on the basis of shape information, which includes a left propagation processing section (121) for propagating, of a plurality of pixel data which construct one-dimensional image data, pixel data specified by shape information to the left, a right propagation processing section (123) for propagating, of the plurality of pixel data which construct the one-dimensional image data, the pixel data specified by the shape information to the right, and a calculator group (131) for calculating the average between an output from the left propagation processing section (121) and an output from the right propagation processing section (123) to generate output pixel data.