An image processing apparatus for performing an image processing on a body cavity image captured in a living body includes: a storage unit which stores information including image information of the body cavity image; a change amount calculator which reads out the image information of the body cavity image from the storage unit and calculates, in the read body cavity image, a pixel value change amount of a pixel of interest with a plurality of surrounding pixels located around the pixel of interest; and a candidate lesion region detector which detects a candidate lesion region in the body cavity image based on calculation result of the change amount calculator.