[SUMMARY] Purpose: To clarify the structure of social support and self-care behavior for prevention of lifestyle-related diseases in middle-aged single men and obtain evidential support for developing lifestyle improvement support guidelines which utilize social support. Method: We conducted semi-structured interviews of unmarried men between the ages of 40 and 60 and qualitatively analyzed self-care behavior, the factors that mediate it, and social support. We then organized the extracted categories and confirmed the resulting structure based on an analytical framework. Results: Self-care behaviors, including “making a conscious realistic effort in one’s life” by directly taking action and receiving instrumental and informational support such as “meals and care for poor physical condition provided by family members and colleagues”, were connected directly with social support or indirectly through mediators of self-care behavior, including “increased interest in one’s body and life along with anxiety about being alone” which was cultivated by receiving social supports including “advice from health care professionals, family members, friends, colleagues, and SNSs”. Conclusion: Self-care behaviors in middle-aged single men included objectively perceiving physical changes in their bodies while continuing to make realistic efforts in their lives through enjoyment of activities such as hobbies, anticipating and experiencing such activities’ effects, and enhancing a sense of control and self-esteem. Additionally, the physical and human environment of the workplace inevitably led to increased health awareness and behaviors. Moreover, in addition to family, informational, emotional, collective, and instrumental support were provided by colleagues and friends, yielding a sense of connectedness and promoting self-care behavior.