1. A relevance analysis device that analyzes a mutual relevance between a plurality of users utilizing a server that allows users to view information provided by target viewed users, the relevance analysis device comprising: a controller that: specifies out of the plurality of users an analysis reference user who serves as a reference for analysis, and an analysis target user who serves as a target for analysis of relevance to the analysis reference user; acquires from the server identification information that uniquely identifies the user, and registration information for specifying the target viewed user registered by the user; based on the identification information and the registration information, specifies a route that spans between the analysis reference user and the target viewed user, the specified route being constituted from at least one component route, the specified route having an origin that corresponds to the analysis reference user and an end that corresponds to the analysis target user, each component route of the specified route having a relationship in which an end-side user of the component route is registered as the target viewed user by an origin-side user of the component route; specifies a number of the component routes that constitute the specified route; for each of the component routes that constitute the specified route, specifies whether the origin-side user is registered as a target viewed user by the end-side user based on the identification information and the registration information; and specifies the mutual relevance between the analysis reference user and the analysis target user based on the specified number of the component routes and based on the number of the component routes in which the origin-side user is registered as a target viewed user by the end-side user.