An image processing apparatus capable of performing good luminance correction without performing a cumbersome process is provided. The image processing apparatus includes an illumination light component estimation unit which calculates an estimated illumination light component of an original image, an estimated illumination light component correction unit which outputs a corrected estimated illumination light component obtained by correcting the estimated illumination light component, and a Retinex processing unit which corrects a luminance component of the original image by dividing the luminance component by the corrected estimated illumination light component.