This study aims to investigate the thoughts of the general population regarding life-sustaining treatment for both oneself and family members and to assess the factors associated with those thoughts. A total of 1,500 individuals participated in this study by completing a questionnaire consisting of self-reporting items with some instructions, basic demographic information, thoughts on life-sustaining treatment, and psychosocial scales. The disease status was calculated using the Charlson Comorbidity Index. The psychosocial scales included the Patient Health Questionnaire-9 (PHQ-9), Generalized Anxiety Disorder-7 (GAD-7), Pittsburgh Sleep Quality Index, and Multidimensional Scale of Perceived Social Support. The majority of participants did not want to receive life-sustaining treatment for both themselves and their families. However, more people wanted life-sustaining treatment for their family members (35.9%) than for themselves (21.6%). Among the basic demographic characteristics, there were significant differences in age, sex, marital status, living arrangements, occupational status, religion, and disease status. Regarding the psychosocial scales, there were significant differences in the PHQ-9 and GAD-7 scores between the group that preferred life-sustaining treatment for family members and the group that did not. The findings suggest that life-sustaining treatment decisions for oneself and for one's family members can be different. We recommend a more clear expression of one's preferences regarding the last moments of one's life, including advance directives.