A route selection assistance system for assisting in selecting a route of a living body lumen for delivering a medical instrument to a site within a living body via the living body lumen via an introduction site, the route selection assistance system comprising a computer main unit, the computer main unit comprising: a receiving section configured to receive an input of site information specifying a target site within the living body as a target of delivering the medical instrument; an image obtaining section configured to obtain image information on an inside of the living body of a target patient as the target of delivering the medical instrument; characterized by: a route extracting section configured to extract a plurality of routes of the living body lumen, the plurality of routes allowing the medical instrument to be delivered to the target site on a basis of the image information obtained by the image obtaining section; a ranking assigning section including a route score calculating section configured to calculate route scores determined according to ease of delivery of the medical instrument at a time of delivery of the medical instrument via the routes and based on lengths of the routes and bending degrees of the routes, and a patient score calculating section configured to calculate patient scores determined according to magnitude of a burden imposed on the target patient by using an invasion degree of the route extracted by the route extracting section, the ranking assigning section assigning rankings to the plurality of routes extracted by the route extracting section by using the route scores and the patient scores; and an output section configured to output the plurality of routes extracted by the route extracting section and the rankings assigned by the ranking assigning section. a receiving section configured to receive an input of site information specifying a target site within the living body as a target of delivering the medical instrument; an image obtaining section configured to obtain image information on an inside of the living body of a target patient as the target of delivering the medical instrument; characterized by: a route extracting section configured to extract a plurality of routes of the living body lumen, the plurality of routes allowing the medical instrument to be delivered to the target site on a basis of the image information obtained by the image obtaining section; a ranking assigning section including a route score calculating section configured to calculate route scores determined according to ease of delivery of the medical instrument at a time of delivery of the medical instrument via the routes and based on lengths of the routes and bending degrees of the routes, and a patient score calculating section configured to calculate patient scores determined according to magnitude of a burden imposed on the target patient by using an invasion degree of the route extracted by the route extracting section, the ranking assigning section assigning rankings to the plurality of routes extracted by the route extracting section by using the route scores and the patient scores; and an output section configured to output the plurality of routes extracted by the route extracting section and the rankings assigned by the ranking assigning section. a route extracting section configured to extract a plurality of routes of the living body lumen, the plurality of routes allowing the medical instrument to be delivered to the target site on a basis of the image information obtained by the image obtaining section; a ranking assigning section including a route score calculating section configured to calculate route scores determined according to ease of delivery of the medical instrument at a time of delivery of the medical instrument via the routes and based on lengths of the routes and bending degrees of the routes, and a patient score calculating section configured to calculate patient scores determined according to magnitude of a burden imposed on the target patient by using an invasion degree of the route extracted by the route extracting section, the ranking assigning section assigning rankings to the plurality of routes extracted by the route extracting section by using the route scores and the patient scores; and an output section configured to output the plurality of routes extracted by the route extracting section and the rankings assigned by the ranking assigning section.