1. An extracting method for use in an apparatus for extracting a blood vessel crossing/branching portion from an image including a blood vessel, the method comprising: a setting step of setting outer circumferential small regions in an outer circumferential portion of an extraction candidate region in the image; a center portion determining step of determining whether or not a coordinate average of outer circumferential portion blood vessels existing in at least three of the set outer circumferential small regions 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, when it is determined in the center portion determining step that the coordinate average is included in the center portion.