1. An image processing apparatus comprising: an image obtaining device which obtains a breast image obtained by radiography of a breast; a mammary gland region extracting device which extracts a mammary gland region from the breast image; an local region setting device which sets a plurality of local regions around pixels belonging to the mammary gland region extracted by the mammary gland region extracting device; a local contrast value calculating device which calculates a plurality of local contrast values in the local regions, for each of the plurality of local regions set by the local region setting device; and an image processing device which applies image processing to the breast image on the basis of the plurality of local contrast values calculated by the local contrast value calculating device.