The purpose of this study is to verify the moderating effect of self-reflection intelligence in the relationship between adverse childhood experience and psychological well-being in adulthood and use it for treatment, counseling, and education. To investigate this, an online questionnaire was distributed to adults in their 30s and 40s on adverse childhood experience (ACE), psychological well-being in adulthood, and self-reflection intelligence. For data analysis, the moderating effect was verified through correlation analysis between variables, multiple regression analysis, and hierarchical regression analysis. The results of this study are as follows. First, adverse childhood experience and psychological well-being in adulthood were found to have a negative relationship. Second, in the relationship between adverse childhood experience and psychological well-being in adulthood, self-reflection intelligence showed a moderating effect. The results of this study suggest that adverse childhood experience has a negative effect on psychological well-being in adulthood. However, the influence of adverse childhood experience can be lowered through self-reflection.