An image processing device (10, 20, 30) configured to synthesize a first image and a second image shot according to a Line by Line system, wherein the first and the second image are obtained by imaging each row alternately in two or more exposure times different in length, the image processing device (10, 20, 30) comprising: a level adjuster configured to adjust a luminance level of the first image and output a corrected first image having a luminance level that is substantially the same as a luminance level of the second image; a movement detector (110, 210) configured to calculate an absolute value of a difference in a pixel value between each pair of co-located pixels in the corrected first image and the second image and accumulate the absolute value on an image block basis, the image block being a plurality of sets of continuous pixels in the corrected first image or the second image to obtain a movement detection amount in each of the plurality of image blocks; a movement blending ratio calculator (120, 320) configured to smoothen the movement detection amount in each of the plurality of image blocks and calculate a movement blending ratio between each pair of the co-located pixels in the image block based on the smoothened movement detection amount; and an image synthesizer (130, 150) configured to generate a movement-adaptive image by synthesizing the co-located pixels at the movement blending ratio wherein the movement blending ratio calculator executes smoothening of the movement detection amount in each of the plurality of image blocks by using an inter-block smoothening filter configured to smoothen the movement detection amount on the image block basis between a plurality of image blocks located near the plurality of image blocks and an inter-pixel smoothening filter configure to smoothen the amounts of detected movements between a plurality of pixels near a target pixel for the accumulating of the absolute value on an image block basis in the corrected first image, wherein a difference in movement detection amount between adjacent image blocks is segmentalized, and the movement detection amount of each pixel is interpolated so that the difference is distributed depending on a distance of each pixel from a center of gravity of the image block. a level adjuster configured to adjust a luminance level of the first image and output a corrected first image having a luminance level that is substantially the same as a luminance level of the second image; a movement detector (110, 210) configured to calculate an absolute value of a difference in a pixel value between each pair of co-located pixels in the corrected first image and the second image and accumulate the absolute value on an image block basis, the image block being a plurality of sets of continuous pixels in the corrected first image or the second image to obtain a movement detection amount in each of the plurality of image blocks; a movement blending ratio calculator (120, 320) configured to smoothen the movement detection amount in each of the plurality of image blocks and calculate a movement blending ratio between each pair of the co-located pixels in the image block based on the smoothened movement detection amount; and an image synthesizer (130, 150) configured to generate a movement-adaptive image by synthesizing the co-located pixels at the movement blending ratio wherein the movement blending ratio calculator executes smoothening of the movement detection amount in each of the plurality of image blocks by using an inter-block smoothening filter configured to smoothen the movement detection amount on the image block basis between a plurality of image blocks located near the plurality of image blocks and an inter-pixel smoothening filter configure to smoothen the amounts of detected movements between a plurality of pixels near a target pixel for the accumulating of the absolute value on an image block basis in the corrected first image, wherein a difference in movement detection amount between adjacent image blocks is segmentalized, and the movement detection amount of each pixel is interpolated so that the difference is distributed depending on a distance of each pixel from a center of gravity of the image block.