1. An extracting method of a blood vessel crossing/branching portion for extracting a blood vessel crossing/branching portion from an image including a blood vessel, comprising: a selecting step of selecting an extraction candidate region from the image; a setting step of setting an outer circumferential small region into an outer circumferential portion of the selected extraction candidate region; a number determining step of determining the number of outer circumferential portion blood vessels existing in the set outer circumferential small region; a center portion determining step of determining whether or not a coordinate average of the outer circumferential portion blood vessels is included in a center portion of the extraction candidate region; and an extracting step of extracting the extraction candidate region as a blood vessel crossing/branching portion according to determination results of the number determining step and the center portion determining step.