A communication method in which an operation, such as authentication, required when a new communication terminal participates in a mesh network is carried out in a more efficient manner. A second communication terminal that has already established an adjacent communication link with at least two first communication terminals, out of a plurality of communication terminals, distributes an adjacent terminal list including terminal identifiers of the first communication terminals along with a temporal key generated by the second communication terminal. One of the first communication terminals that received the adjacent terminal list and the temporal key distributes adjacent registration information, which is generated using a second temporal key. The other one of the first communication terminals that received both the adjacent terminal list and the adjacent registration information determines whether the terminal identifier of one of the first communication terminals is included in the adjacent terminal list, and whether the first temporal key distributed along with the adjacent terminal list matches with the second temporal key used for generating the adjacent registration information. If both determination results are affirmative, one of the first communication terminals is authenticated.