A network system connects with processes P1 to P5 that can mutually send and receive a broadcast message specified with no destination and a message specified with a specific process portion and change their states to parent or child processes. For example, process P1 is a parent process and processes P2 to P4 are child processes. When processes P1 to P4 constitute a group, each of child processes P2 to P4 stores parent process P1. Parent process P1 stores each of child processes P2 to P4 that store itself (P1). When process P5 in another group is connected, parent process P1 exchanges a message with process P5 for negotiation to determine either to be a parent process and change the other to a child process.