Tentatively shared data is divided into a refining block and a disposable block, the refining block is agitated by a humming distance amplification effect by the both to extend a humming distance, a transmitter (1) transmits this agitation data as a Vernam cipher by means of disposable data, and a receiver (2) decodes the received Vernam cipher in its disposable block, compares data that has agitated it own refining block with a humming distance, and judges whether sharing is possible or not.