Corporate downsizing situations represent an important condition under which employees may experience a breach of the psychological contract that had been maintained between the company and its employees, and consequently, significant changes may occur in the trust that employees feel toward the company and management. In this regard, the trust perceived by surviving employees can be an important factor that may moderate or mediate the relationship between job insecurity and job performance experienced during the downsizing process; however, few studies have focused on this variable. From this standpoint, this study analyzes the relationships among job insecurity felt by surviving employees in firms that have undergone downsizing, their reactions, and job performance, with particular emphasis on empirically examining how the trust factor perceived by surviving employees toward management moderates the relationships among these variables. The survey results confirmed that job insecurity felt by surviving employees in downsized firms had a negative impact on their attitudes toward the company and management, including trust and organizational commitment. However, contrary to expectations, the relationship between job insecurity and job performance was found to be positive. Meanwhile, the moderating effect of the trust variable was manifested more strongly through employees who perceived low trust in management. Specifically, the negative impact of job insecurity on organizational commitment was more pronounced among employees who perceived low trust, while the positive impact of job insecurity on job performance was also greater among employees with low trust. The implications of these analytical results and the limitations of the study were discussed.