The purpose of this paper is to build up a pragmatic account of using and realising metaphor, particularly shown in public communication such as commercial advertisements. According to the traditional point of view, metaphor is a “figure of speech in which a linguistic expression normally belonging to one field of reference is extended analogously to another”(Huang 2012: 191-192). Beyond this way of rhetorical perspective on metaphor, however, this paper pursues to re-recognition of the linguistic nature of metaphor with a more active insight(e.g., from a viewpoint based on experientialist epistemology) and seeks the rational explanation of metaphor in accordance with it. Especially, in some influential studies of cognitive pragmatics(i.e., Relevance Theory: RT) such as Sperber and Wilson(1995, 2006), Yus(2009) and Carston(2000, 2002, 2010), metaphor has been evaluated as a linguistic mechanism which shows ordinary language users’ cognitive reasoning and conceptualization abilities, not just as a method of expression. Based on the RT approach to metaphor, this paper presents an alternative way of explaining metaphor used in public communication, the goal of which is to perform argumentation for persuading consumers to purchase an advertiser’s products, services and ideas.