The purpose of this study is to evaluate the usefulness of salivary alpha(α)-amylase activity (sAMY) using a chemical sensor as a mental health index in human for a human-machine interface. Seventy healthy subjects were enrolled (12-13 yr). A General Health Questionnaire (GHQ-28) and a State-Trait Anxiety Inventory (STAI) were conducted as subjective evaluations; from these the all subjects were divided into two groups; high and low stress. High stress group determined from either GHQ-28 or STAI showed significantly higher sAMY than those in low stress group. Multiple regression analysis using sAMY as the dependent variable was applied between sAMY and both mental health indexes. A relationship was found between the high stress group and the sAMY. These results suggested that sAMY is a useful index for screening of healthy subjects not having any particular mental health disease but at risk of developing severe mental health conditions. The chemical sensor of the sAMY might be a useful method as human-machine interface.