The problems (lack of storage, system trouble, problem of power supply, etc.) in a single cloud with increase the use of clouds are being raised. For these reasons, multi-clouds are needed. In multi-clouds, cloud providers as different forms of systems with different authentication systems demand an authentication to a user. So users using multi-clouds have different authentication ID and password for each cloud because they have to authenticate differently for each cloud. As a result, users are inconvenient to manage multiple of authentication IDs and passwords and users' authentication information exposed whenever they access to multi-clouds is in a poor security.