An intermediation method used in an intermediation system that includes an intermediation device determining a permission for application services requiring user authentication on a network, where in response to a user request, a first account used for a first service and a second account used for a second service, and a registration request for using the linking service linking the first application service and the second application service are associated with each other, when the two accounts are valid, as accounts usable in a linking service, an association between the first and second services is stored in the intermediation device, and when the user makes a request to use the linked services, that use is controlled by a query to the intermediation device regarding whether the account is associated as able to use the linking service.