1. An image restoration apparatus comprising: a first image generator for generating a first image; a detector for detecting a degradation information of the first image; a filter generator for generating a degrading filter and a transposed filter of the degrading filter based on the detected degradation information; a second image generator for generating a second image by use of the first image and the degrading filter; a residual image calculator for calculating a residual image from the first image, the degrading filter and the second image; a gradient image calculator for calculating a gradient image of the residual image by a convolution operation of the transposed filter and the residual image; and a corrector for correcting the second image by use of the gradient image calculated by the gradient image calculator.