The purpose of this study is to deeply understand the causes of addiction of the addicted adolescents of smartphone. Colaizzi's phenomenological study method was applied to analyze the causes of the addiction caused by the addicts'. The results of the study were confirmed 63 constructive meanings in the meaningful data expressed in the participants' experiences, Based on them, they were derived as 26 subjects, 8 subject groups and 2 categories. The causes of addiction were 'Personal psychological factor', 'Behavior habit factor', 'Social relation factor' and 'Internet smart phone factor'. Psychological, physical, interpersonal and everyday life changes were the results accompanied by causes of addiction. Through this study, the causes of addiction revealed in the participants' experiences are expected to be applied to the client-centered therapy of the smartphone addiction counseling process.