An authentication system, a user information extraction apparatus, and a user information migration method. The authentication system acquires user information for authenticating a user who uses a device and transmits the acquired user information to the information processing system and the information processing system stores in one or more memory common user information for authenticating a common user who uses the device and another device different from the device, receives the user information from the user information extraction apparatus, and adds the received user information to the common user information stored in the one or more memory.