The emissions of greenhouse gases (CH₄, N₂O) from Johkasou were monitored at three sites for over a year, and the seasonal variabilities were analyzed. Based on the annual average emissions, about 90% of CH₄ was emitted from the anaerobic tank and about 80% of N₂O was emitted from the aerobic tank. CH₄ emissions increased when the amount of influent DO into the anaerobic tank decreased. It is caused that the amount of CH₄ production increases due to the progress of anaerobic treatment at the bottom of the anaerobic treatment tank. On the other hand, N₂O emissions increased when BOD and NH₄-N in the tank increased as the water temperature rise period. It is caused that nitrification reaction (nitrite oxidation) in the aerobic tank does not proceed promptly due to elution of BOD and NH₄-N from the stored sludge in the Johkasou.