An image processing device includes; a lesion candidate region detecting section that detects a lesion candidate region based on at least one color signal in a medical image including a plurality of color signals; an incidental region detecting section that detects an incidental region that arises because of incidental attributes accompanying a lesion from the medical image; and a detection standard changing section that changes a detection standard when detecting a lesion from the lesion candidate region in accordance with a detection result of the incidental region.