The prevent invention can prevent roughness in an image and reduce contouring and coding distortion in the image. The image processing apparatus according to the present invention reduces distortion in an input image, and includes: a masking signal generating unit 101 that generates a masking signal for reducing the distortion; and a masking signal adding unit 102 that adds the masking signal to the input image, wherein the masking signal generating unit 101 includes: a level difference processing unit 105 that smoothes a level difference between pixel values of pixels in the input image; a difference calculating unit 106 that calculates a difference between the input image and an image which has been processed by the level difference processing unit 105; and a random number setting unit 108 that sets an amplitude, creates a is random number having the set amplitude, the amplitude decreasing, as the difference approaches a predetermined value.