Abstract: When transmitting a pass-word updating request transmitted from a local host to a remote host via a network, both a present pass-word and a new pass-word are enciphered with the present pass-word of a user as a key of enciphering and then are transmitted. The remote host fetches the present pass-word from a pass-word table on the basis of a user ID and then deciphers the pass-word updating request transmitted thereto with the resultant present pass-word as a key of deciphering. Then, only when the specified present pass-word in the pass-word updating request frame matches with the present pass-word registrated in the pass-word table, the remote host updates the present pass-word into the specified new pass-word.