At present

the context free grammar and the pushdown automaton are the usually used formal systems in research for context free languages

correspondently

the regular grammar and the finite automaton are usually used in research for regular languages. The correspondency between the symbols in regular grammar and the symbols in finite automaton is relatively evident. In other words

it is easier to transform one to the other between these two systems

and people may have a more accordant comprehension when they observe the characteristics of a language in these two systems. But the correspondency between context free grammar and pushdown automaton is not so evident as that between regular grammar and finite automaton. The infinite state automaton introduced in this paper is also a kind of recognizing system for context free languages

however

there is also an evident correspondency between context free grammar and infinite state automaton similar to that between regular grammar and finite antomaton

thus bringing the benefits to the research of context free languages.