An ID bridge service system manages a type and assurance of identity information required for provision of service by an application service system and a type and assurance of identity information managed by plural authentication service systems, and is provided with a selecting measure that selects an authentication service system that manages identity information corresponding to the identity information required for the provision of the service by the application service system out of the plural authentication service systems when a request for authentication is received from the application service system and a requesting measure that requests the selected authentication service system to authenticate.