A trunk-sharing system that controls an user's authority to use a predetermined area of a vehicle by issuing a predetermined authentication information to a user terminal, the trunk-sharing system including a server configured to: acquire a first information on a permission of using the predetermined area of the vehicle from a first user who owns the vehicle; provide the first information such that the first information acquired from the first user of each of a plurality of vehicles is able to be detected by a second user other than the first user; acquire a second information on a request for a use of the predetermined area which is an information from the second user who has accessed the provided first information; and issue an authentication information for locking and unlocking the predetermined area to a terminal of the second user based on the first information and the second information.