Effective utilization of solar thermal energy is essential for reducing CO_2 emission caused by the Heating, Ventilation, and Conditioning system of a building. A solar-assisted heating and cooling system was installed in an office building in Mie prefecture in December 2009. The total floor area of the building is 2,400 m^2, and the system consists of a solar collector (110 m^2), thermal storage tank (4.9 m^3), and triple-effect absorption machine (527 kW cooling, 290 kW heating). Examination of the system behavior and performance has been conducted since January 2010. The results are summarized as follows. 1) The solar fraction is 16% during the cooling period and 8% during the heating period. 2) The gas reduction rates are 11% and 9% for the cooling and heating periods respectively. 3) The system-COP (primary energy base) for a system operated with solar thermal energy and gas is 10% higher than that for a system operated with gas only. 4) It is possible to use the collected hot water at around 65℃ as a heat source for driving the absorption chiller.