Provided are a diagnosis assisting device that facilitates a user to grasp a difference of an affected area to perform a highly precise diagnosis assistance, an image processing method in the diagnosis assisting device, and a program. An image processing method in a diagnosis assisting device that diagnoses lesions from a picked-up image includes (A) performing an image processing on the picked-up image. In (A), a peripheral area other than a diagnosis area that has a high probability as diseases in the picked-up image is set to be a measuring area when an image correction is performed.