The purpose of this study was to examine the relationships between smartphone addiction of middle school students and smartphone usage types, depression, attention deficit hyperactivity disorder (ADHD), stress, interpersonal problems, and parenting attitude. This study was also performed with the aim of verifying the relationships among depression, ADHD, perceived stress, interpersonal problems, and parenting attitude, which are predictors of smartphone addiction. The subjects of this study were 487 local middle school students (234 males and 253 females). The measurement instruments used were the smartphone addiction scale, depression scale (PHQ-9), ADHD scale (K-ARS), perceived stress scale (PSS), interpersonal problem scale (KIIP-SC), and the parenting attitude scale. This study identified the relationships between the variables with correlation analysis and examined the predictors of smartphone addiction with hierarchical multiple regression analysis. According to the study results, the factors that influenced smartphone addiction were gender, stress, and interpersonal problems. In addition, when the confounding variables of smartphone addiction were controlled to examine the effects of smartphone usage types on smartphone addiction, social media use and music/videos were found to have a positively significant effect on smartphone addiction while study had a negatively significant effect. The order of the usage types with the highest influence on smartphone addiction was enjoying music/videos, social media use, and study. This suggests that selective intervention depending on the main smartphone usage type can be effective.