A communication terminal apparatus is used in a communication system including at least one first terminal having an optical communication section to optically communicate with one other first terminal and at least one second terminal having a network communication section to communicate with a plurality of other second terminals through a network. In the communication terminal apparatus as a relay terminal, an optical communication section optically communicates with the at least one first terminal. A network communication section communicates with the at least one second terminal through the network. A received information sending section sends information received from the optical communication section to the network communication section, and sends information received from the network communication section to the optical communication section.