The number of school teachers in Japan that take sick leave due to mental illness temporarily decreased below 5,000. However, it exceeded 5,000 after the academic year of 2013 and has remained at a high level since then. Different strategies that are optimal for individual teachers are required for improvement of their mental health, and one effective approach may be physical activity. The present study examined the influence of physical activity on the mental health of elementary school teachers. A questionnaire survey of full-time teachers (n=700) working in public schools was conducted using the General Health Questionnaire (GHQ28) and the International Physical Activity Questionnaire; Japanese version (IPAQ-Long Version). Valid responses (n=542) were analyzed using the Statistical Package for the Social Sciences. The participants included 187 men and 352 women ranging in age from 22-60 years (mean 42 years). The length of career as a full-time teacher (number of years after being first officially employed) was 0-39 years. The average period of teaching experience was 17.3 years. The level of mental health was assessed using the GHQ. The results indicated that 45.9% of the participants had some mental problems. Especially, scores for “somatic symptoms” were significantly higher in female teachers than in male teachers. The mean amount of total physical activity determined using the IPAQ-LV was 2,029.0 MET-minutes per week. Physical activity in the worksite accounted for approximately 50% of the total. In the context of “leisure”, the amount of physical activity for male teachers was significantly greater than for female teachers. Moreover, the influence of physical activity examined using multiple regression analysis confirmed a model for female teachers in which a significant pathway was identified from worksite physical activities to “somatic symptoms,” “anxiety and insomnia,” and “social dysfunction”. Furthermore, a significant pathway was identified from physical activity during housework and garden work to “social dysfunction”. This study reconfirmed the deterioration of mental health in elementary school teachers. The limits of this study and future issues including the investigation of confounding factors related to the results and the need for longitudinal research were also discussed.