Provided are an authentication method, authentication system and a terminal device in which the authentication of a non-participating third node is can be simplified and can be executed in the case of multicast by using an authentication ticket in a distributed processing network system, the non-participating third node being intended to access each of the nodes, including a first and a second node, constituting a workgroup. The first node that has already participated in the workgroup authenticates the third node intended to participate in the workgroup and issues the authentication ticket including the signatures of both nodes, and when the authentication ticket is submitted to the second node, the second node permits the third node to access, without password-based-authentication, by authenticating the first node and the second node which have signed the authentication ticket.