In Japan, mergers of cities, towns, and villages have occurred rapidly as a result of the Special Law on the Merger of Municipalities, enacted in 2005. These mergers may impact civil servants’ psychological adjustment. We developed the Municipal Merger Stress Questionnaire (MMSQ) to measure the impact of the municipal mergers and collected responses from 570 employees who had experienced a municipal merger (Study 1). We examined the relationships among the impact of municipal merger, Stress Responses, Self-concept (self-esteem and interpersonal dependency), and Social Support (Study 2). Two factors (Increased Workload and Worthlessness) were derived from the MMSQ in Study 1. Additionally, a structural equation model showed that the impact of the loss of value of their job (Worthlessness) related to the psychological stress responses, while job discretion did not differentiate an entire stress situation in Study 2. The result implies that psychological aspects of interventions focused on worthlessness are required to maintain good mental health of public servants at workplaces.