The purpose of this study is to suggest for utilization of supporters to promote public libraries. To achieve the study purpose, in-depth interview with nine public library supporters of two public libraries was conducted. The data were analyzed using a qualitative method. The order in which the data analyzed is as follows: segmenting, first coding, in-depth coding, and theme discovery. According to the study results, the followings were suggested for the operation of public library supporters: 1) needed to assign roles based on supporters’ capabilities and personal characteristic, 2) needed proactive role by the librarian in charge, 3) needed proactive role by the public library, 4) needed adequate rewards, 5) needed prior education about the public library.