A system 100 includes a first service providing part 110 for providing a first service, and a second service providing part 120 for providing a second service. The first service providing part 110 transmits a first individual ID that is associated with a common ID included in an ID information provision request and that is for identifying a user in the first service, to a user terminal. The second service providing part 120 receives a service ID for identifying the first service, the first individual ID and the common ID from the user terminal, and transmits the service ID and first individual ID having been received with the common ID associated with a second individual ID that is included in an ID information acquisition request and that is for identifying a user in the second service, to a user terminal