Aims: This study aimed to analyze the process in which individual values and beliefs affected social distance against people with mental illness by mediating cognition, based on applying the justification–suppression model to the stigma of mental illness. Methods: An online survey was conducted with 491 adults aged 20 to 64 years. Their sociodemographic characteristics, personal values, and beliefs, justification for discrimination, and social distance were measured to assess their perceptions of, and behaviors towards, persons with mental illness. Path analysis was performed to examine the magnitude and significance of the hypothetical relationship between variables. Results: Protestant ethic values and morality significantly affected the justification of inability and dangerousness and attribute responsibility. Excluding attribute responsibility, the justification of inability and dangerousness significantly predicted social distance. In other words, the higher the Protestant ethic values, the higher the morality of binding, and the lower the morality of individualizing, the higher the level of justification based on inability and dangerousness. Such justification has been found to increase social distance from persons with mental illness. In addition, mediating effects were the largest in the path of the morality of binding → justification of dangerousness → social distance. Conclusions: The study proposes various strategies to deal with individual values, beliefs, and justification logic to reduce social distance against those with mental illness. These strategies include a cognitive approach and empathy, both of which inhibit prejudice.