PURPOSE: To provide a structure for plural automaton sets including plural interfaces which process plural interleaved messages.

CONSTITUTION: Plural automatons A constituting a set E communicate with each other and with environments on the outside of this set only in the asynchronous communication mode. Each automaton consists of a combination of plural sub-automatons S, and each sub-automaton is provided with at most one interface I on the outside of the automaton. All sub-automatons pertaining to the same automaton use a single pseudo-synchronous communication mode to communicate with each other, and thereby, events constituting the communication are synchronized with environments on the outside of sub-automatons communicating each other and are made asynchronous with those on the inside of these sub-automatons. Each sub-automaton consists of a combination of plural fundamental automatons called bricks B, and bricks pertaining to the same sub- automaton communicate with each other only in the synchronous communication mode.