1. An image processing device for adding respective mutually corresponding pixels of an original image generated from original information and of a smoothed image generated from the same original information and reduced at least in streak artifact with weighting using a weighting coefficient and generating a target image that an edge of a structure is maintained and the streak artifact is removed, comprising: a function shape determination unit that determines a shape of a nonlinear function on the basis of feature amounts of the original image and the smoothed image; and a weighting coefficient calculation unit that calculates the weighing coefficient on the basis of the nonlinear function.