1. An image processing device comprising: an image acquiring unit that acquires a plurality of images obtained by capturing a same subject plural times; a reference image selecting unit that selects, as a reference image, one image of the plurality of images; a transformed image generating unit that, for a non-reference image that was not selected by the reference image selecting unit, generates a transformed image that is transformed by making a position of an image of a same subject correspond to the reference image; a noise reduced image generating unit that carries out noise-reduction processing on the reference image and generates a noise reduced image; an intermediate composite image generating unit that sets a weighting coefficient of the reference image with respect to the transformed image such that, the greater an absolute value of a first difference in pixel values of corresponding pixels of the reference image and the non-reference image, the greater the weighting coefficient, and generates an intermediate composite image by carrying out combining processing of the reference image and the transformed image on the basis of the set weighting coefficient per pixel; and a final image generating unit that sets a weighting coefficient of the noise reduced image with respect to the intermediate composite image such that, the greater an absolute value of a second difference in pixel values of corresponding pixels of the reference image and the intermediate composite image, the smaller the weighting coefficient, and generates a final image by carrying out combining processing of the intermediate composite image and the noise reduced image on the basis of the set weighting coefficient per pixel.