An image processing device includes: a luminance saturation position detection unit which detects a luminance saturation position to produce a light source image; a flare model production unit which produces a flare model image based on the light source image and optical characteristics data of the optical system; a flare position setting unit which sets, as a flare position, a predetermined image position in the captured image and located near the luminance saturation position and on a side of an optical axis relative to the luminance saturation position; a flare model luminance adjustment unit which produces the estimated flare image by adjusting luminance gain of the flare model image, based on a relationship between a luminance value of the captured image at the flare position and a luminance value of the flare model image at the flare position; and an unnecessary light subtraction unit which subtracts the estimated flare image from the captured image.