Objectives: The purpose of this study is to examine the effects of symptoms of dementia elderly on the primary caregiver’s depression. In addition, moderating effect of family support was examined. Based on the results, the necessity for intervention in the level of social welfare as a way to mitigate primary caregiver’s depression was suggested. Method: In order to accomplish these purposes, a total of 197 who are spouse and adult-children of dementia elderly using day care facilities or services in Seoul, Gyeonggi, Busan province, South Korea were utilized. Data were analyzed by frequency analysis and descriptive statistics, regression model analysis with SPSS 18.0. Results: In case of analysis results, the mean value was reported 0.9 out of four point about primary caregiver’s depression and the mean value of family support was reported 3.34 out of five point. And besides, the analysis result of dementia elderly’s symptoms showed that prevalence of depression/dysphoria were 62.2%, prevalence of aberrant motor were 61.3%, prevalence of apathy/indifference were 56.6%. Crucial findings are as follows: the symptoms of dementia elderly was significantly associated with the primary caregiver’s depression. At the same time, family support significantly influenced lower level of the primary caregiver’s depression. While, in the relationship between the symptoms of dementia elderly and the primary caregiver’s depression, family support has a moderation effect by important protection factor. Conclusions: From these findings, the necessities to provide the care service for dementia elderly to help improve symptoms of dementia as well as the policy and service to manage the mental health of the family as primary caregiver were suggested. Also, the necessities to provide the family therapy program to improve the relationship with family members were suggested.