The purpose of this thesis is to examine a metaphor from the angle of the observation. That way, the feature as the function of the metaphor will be brought into shaper focus. A metaphor involves "cutoff" and "connection" processes at the same time while duplicating the meaning of the expression. In other words, a metaphor contains two contradictory elements at the same time. This article analyzes the function of medium of the metaphor from the perspective of social theory. The thesis also argues that paradoxes and tautologies, etc. are a fundamental principle of a metaphor by quoting Luhmann's theory.