A key managing system including information transmitting apparatus which transmits a date and time when secrecy protection is ended to a key controlling apparatus. The key controlling apparatus searches a key control table for an encryption key associated with a decryption key and the date and time. The key controlling apparatus transmits an encryption key from the search to the information transmitting apparatus. The key controlling apparatus discloses a decryption key for the present date and time to an information receiving apparatus in response to a request for a decryption key. The information transmitting apparatus, upon receipt of the encryption key, encrypts information using the encryption key and transmits the encrypted information to the information receiving apparatus. The information receiving apparatus, for the present date and time matching with the date and time, acquires a disclosed decryption key and decrypts the encrypted information by using the decryption key.