<p>This article focuses on how the term kuchi komi (meaning "word of</p><p>mouth") came to be used in advertising theory in Japan in the early 1960s from</p><p>a view of conceptual analysis.</p><p> So far, little attention has been given to kuchi komi in media history and</p><p>advertising history. This is because kuchi komi is a medium that leaves no</p><p>material or institutional traces. This article aims to provide a history of kuchi</p><p>komi by focusing on it as a concept, and analyzes how it came to be presented</p><p>as an advertising tool. We mainly analyze textual data that presented kuchi</p><p>komi as an advertising tool in the early 1960s.</p><p> As a result, we revealed:( 1) the Reading Social Survey conducted during</p><p>1956 played an important role in the spread of the "opinion leader" concept in</p><p>the advertising industry, and( 2) the term kuchi komi was newly presented as</p><p>an advertising tool in the early 1960s in relation to the "opinion leader" concept.</p>