The climate in Japan is generally cool/dry in winter and hot/humid in summer. Winter season is from December to February in Japan. January is the coldest month. We measured indoor air conditions; air temperature, humidity and carbon dioxide (CO2) during 12 months at the office room of one manufacturing industry (800 workers). The office hour at this office is from 8:30 to 17:30. Average mean value (±standard deviation) of room air temperature in January was 20.3±3.1°C, humidity was 32.8%±3.5% and CO2 was 924.5±478.2 ppm. Average room air temperature at office hour was 24.0±0.8°C, maxi/mini air temperatures were 25.1/22.2°C, average humidity was 38.8%±2.5%, maxi/mini humidity was 41.3/33.7% and average CO2 was 1350.9±228.3 ppm, maxi/mini CO2 were 1563/792 ppm. Setting room air temperature of 25°C comprised the highest frequency at air conditioners at this office. Regarding the recommend levels for air conditions in office buildings, air temperature is 17°28°C, relative humidity is 40˜70% and CO2 is 1000 ppm during all seasons. As Conclusion, the room air temperatures at office hour were rather high and humidity levels were low. We recommend setting room air temperature level for energy conservation and health is 17˜20°C, and humidity is about 50% in winter.