In this paper, we present findings about factors that influence private information disclosure activities in social networking service (SNS). Our study is based on two data sets: (1) Survey Data, responses to a questionnaire consisting of items such as users' privacy settings, motivations of using SNS (motivations), and risk awareness, and (2) Public Data, consisting of user profiles that were opened to the public. Openness score is calculated from the number of disclosed items. We study influential factors and their rankings at varying openness scores and disclosure scopes. Our findings reveal that, gender, profile photo, certain motivations, and risk awareness highly affect private information disclosure activities. However the ranking of influential factors is not uniform. Gender and profile photo have greater influence, however their influence becomes lower and loses significance as openness is getting higher, falling behind motivations and number of friends. We also observe consistent tendencies between both data.