A cooling/heating apparatus using a cogeneration system is disclosed. The cooling/heating apparatus includes a discharge-side refrigerant heating unit which supplies heat of exhaust gas generated from an engine to a discharge-side refrigerant line connected to a compressor included in a cooling/heating unit, a suction-side refrigerant heating unit which supplies heat of cooling water used to cool the engine and the heat of the exhaust gas to a suction-side refrigerant line connected to the compressor, a discharge-side refrigerant temperature sensor which senses a temperature of a refrigerant passing through the discharge-side refrigerant line, and a bypass unit which bypasses the exhaust gas heat supplied to the discharge-side refrigerant line via the discharge-side refrigerant heating unit when the refrigerant temperature sensed by the discharge-side refrigerant temperature sensor is not lower than a predetermined temperature, to cut off the supply of the exhaust gas heat or to adjust an amount of the supplied exhaust gas heat. The exhaust gas heat and cooling water heat are appropriately distributed to both the suction and discharge sides of the compressor, so that it is possible to achieve an enhancement in heating performance and an enhancement in system efficiency.