A nail contour detecting device including a processor, wherein the processor obtains first feature point data of a first nail contour which is a nail contour detected from a first nail image obtained by imaging a nail of a finger or a toe, and second feature point data of a second nail contour which is a nail contour detected from a second nail image obtained by imaging a nail of the same finger or toe as the first nail image; and the processor obtains one nail contour based on the first feature point data and the second feature point data.