In order to examine the cost-benefit of mental health care activities in the workplace, the total costs of the fiscal year 2005, during which the old-type mental health care was conducted, and those of the fiscal years from 2006 to 2008, during which the new-type mental health care was conducted according to the governmental guidelines of each year, were compared using about 3,000 workers in a particular workplace in 2005. The total cost comprised the sum of the medical fees, the payment compensation for sick absences, and expenditures for health care activities of mentally ill health workers. The total costs from 2006 to 2008 were not markedly different from those in 2005, and the benefit due to new-type activity was not shown. However, the following was found: payment compensation for sick absences accounted for 60% of the total cost; personnel expenses which were a large part of the expenditure of health care activities largely changed over the years because of the age structure of the staff in charge. The results show that a cost-benefit analysis may be a useful tool for examining health care activities in the workplace for various members in the workplace although health care issues usually tend to be solved by specialists.