1. An image processing apparatus to generate a moving image with reduced noise, comprising: an image processor configured to: determine, each time an input image is input, whether a change amount of the motion of a pixel value distribution in the input image and an output image that is output, is smaller than a predetermined threshold value; supply a value that becomes larger as the number of times the motion change amount is sequentially determined to be smaller than the predetermined threshold value becomes larger, the value serving as a mixing ratio of the output image in mixing of the input image and the output image; and generate a mixed noise reduced moving image by mixing the input image and the output image based on the mixing ratio; wherein the image processor mixes, each time the input image is input, the input image and the output image based on the supplied mixing ratio and outputs the mixed noise reduced moving image.