This study examined the occupational stress experienced by office worker and exercise instructor working in the Japanese fitness club and the association of these occupational stressors on mental health and the influence of support of superiors and colleagues on worker’s mental health. The survey was conducted on 488 workers in the capital area sports facilities in Japan, among which 426 valid respondents (219 office staff and 207 instructor staff) were grouped and data were analyzed. The survey included (1) Occupational stress measured by the New Brief Job Stress Questionnaire, (2) Mental health measured by General Health Questionnaire. To examine associations between job stress and mental health, t-tests and linear regression analyses models were conducted. As a result, the two groups showed different occupational stress factors. For office staff group, the quantitative demand, qualitative demand, and meaning of job had a stronger relationship with mental health. For instructor staff group, the qualitative demand, interpersonal relationships, and job aptitude had a stronger relationship with mental health. Superior support showed a buffering effect on interpersonal relationships and mental health for office worker group, and colleagues support showed a buffering effect on job insecurity, quantitative demand, and work circumstances for instructor staff group.