In order to ensure security even when packet communication is performed using a plurality of communication paths of a public network, a transmitter stores a first communication pattern. First and second communication units perform packet communication with third and fourth communication units. The packet communication is performed in accordance with the first communication pattern, with dummy packets being inserted into at least one of the groups of packets to be transmitted. A processor restores original data from valid packets, which are remaining packets after the dummy packets are removed, in accordance with a second communication pattern.