To provide a information communication system in which the enforcing of secrecy is attained by using a different cryptographic key in accordance with an other transmission party and enabling changing a cryptographic key as necessary.

A receiving end generates a first key (public key) and a second key (secret key) which is made a pair with the first key in a key generating means 11 and transmits the first key to a transmitting end. The transmitting end performs encryption in which the first key from the receiving end is used in an encryption means 14 and transmits the enciphered information obtained by this encryption to the receiving end. Since the the enciphered information are the information ciphered by the first key generated in the receiving end, the information can be decoded only by the second key (generated in the receiving end) corresponding to the first key. The receiving end decodes the enciphered information from the transmitting end by using the second key generated in the key generating means 11.