A radio station equipped with an array antenna, when transmitting an
information symbol sequence to a particular radio station, uses a
plurality of vectors, which are produced based on a propagation channel
characteristic established between these radio stations, to
simultaneously transmit a plurality of symbol sequences, which include
the information symbol sequence, by way of vector multiplexing, thereby
causing the particular radio station to receive the information symbol
sequence, while causing other radio stations of different propagation
channels to simultaneously receive a part or all the plurality of symbol
sequences. Thus, when data is transmitted to a particular radio station
via a radio communication channel, the concealment of information can be
secured with a high level of security.