We developed a system for measuring emissions from stored slurry by using a floating dynamic chamber. CH4, CO2, N2O and NH3 emitted from the storage tank of a dairy cattle farm in eastern Hokkaido were measured during summer 2008 (7/16–8/6), fall 2008 (10/2–10/26), spring 2009 (6/2–6/21) and winter 2009 (3/11). Average daily gas emission rates in summer, fall and spring were, respectively, 54.8, 54.2 and 34.3 g/m2 for CH4; 602, 274 and 254 g/m2 for CO2; 55.4, 68.2 and trace mg/m2 for N2O; and 0.55, 0.73 and 0.46 g/m2 for NH3. CH4, CO2 and NH3 emission rates during the brief measurement period in winter were reduced to 1/4, 1/23 and 1/2, respectively, of summer emission rate levels. All gas emissions showed diurnal fluctuation and were greatest during the daytime, when the ambient temperature rose. CH4, NH3 and CO2 emissions increased significantly during the daytime, and the daily emission (in grams) of each gas was positively correlated with maximum daily temperature. According to the combined spring, summer and fall measurements, the CH4, N2O and NH3 annual emission factors were 1.42% (g CH4/g volatile solids), 0.02% (g N2O-N/g total N) and 0.43% (g NH3-N/g total N), respectively.