To provide an image processing device, an imaging device, and an image processing program that are capable of reducing unevenness of a signal-to-noise ratio in an image.

An image processing device comprises an image processing unit 140 that acquires image data, selects pixels to be added for each target area including a plurality of pixels adjacent to each other in accordance with luminance of a pixel included in the target area, and calculates an addition average of pixel values of the selected pixels.