To verify a group key in the case of delivering the group key and to prevent an illegal terminal from subscribing to the group.

A base station 10 encrypts a group key and a random number and transmits the result to a terminal. The terminal receiving the group key from the base station 10 encrypts character strings produced, therein by using a public key of the group key, decodes it by using a private key of the group key so as to verify the group key, depending on whether or not the character string before the encryption is agrees matches with that after the decoding. Only when they agree, the terminal transmits a group key receipt signal to the base station 10. When no agreed signal is obtained, the terminal does not transmit the receipt signal to the base station 10. The base station 10 repeatedly transmits the group signal to a terminal that does not send the receipt signal. Since terminals do not request transmission of the group key in this method, the illegal terminal is prevented from subscribing to the group.