Mathematics has an aspect as a common language to describe every science and scientific technology, and which is nothing but a method for rigorous and elaborate consideration. As there would be a physical phenomenon and an economical one, both of which is described by one differential equation, it would be possible to formulate phenomena in various fields in the abstract as one problem in mathematics.That is, clarifying underlying mathematical structures of various practical phenomena and describing their nature rigorously and systematically as well as the investigation of mathematical theory itself are main objectives in mathematical science.