A gas heat pump system comprising: an air-conditioning module comprising a compressor, an outdoor heat exchanger, an expansion device, an indoor heat exchanger, an auxiliary heat exchanger, and a refrigerant tube, characterized by an engine module comprising an engine in which a mixed gas of a fuel and air is burned to provide power for an operation of the compressor, wherein the engine module comprises: a mixer in which the air and the fuel are mixed to be discharged; a turbocharging device configured to receive the mixed gas discharged from the mixer so as to compress and discharge the mixed gas; an intercooler configured to receive the mixed gas compressed in the turbocharging device so as to cool the mixed gas in a heat-exchange manner to increase in density, thereby discharging the mixed gas; a regulator configured to receive the mixed gas discharged from the intercooler so as to control an amount of mixed gas and supply the mixed gas to the engine; and an exhaust gas heat exchanger configured to heat-exchange an exhaust gas discharged from the engine with cooling water, wherein the auxiliary heat exchanger is capable of performing heat-exchange between the refrigerant and the cooling water from the engine, and wherein the exhaust gas heat exchanger has one side, through which the exhaust gas is introduced, and the other side through which the exhaust gas is discharged and which is lower than the one side so that the one side is disposed to be inclined downward to the other side. an air-conditioning module comprising a compressor, an outdoor heat exchanger, an expansion device, an indoor heat exchanger, an auxiliary heat exchanger, and a refrigerant tube, characterized by an engine module comprising an engine in which a mixed gas of a fuel and air is burned to provide power for an operation of the compressor, wherein the engine module comprises: a mixer in which the air and the fuel are mixed to be discharged; a turbocharging device configured to receive the mixed gas discharged from the mixer so as to compress and discharge the mixed gas; an intercooler configured to receive the mixed gas compressed in the turbocharging device so as to cool the mixed gas in a heat-exchange manner to increase in density, thereby discharging the mixed gas; a regulator configured to receive the mixed gas discharged from the intercooler so as to control an amount of mixed gas and supply the mixed gas to the engine; and an exhaust gas heat exchanger configured to heat-exchange an exhaust gas discharged from the engine with cooling water, wherein the auxiliary heat exchanger is capable of performing heat-exchange between the refrigerant and the cooling water from the engine, and wherein the exhaust gas heat exchanger has one side, through which the exhaust gas is introduced, and the other side through which the exhaust gas is discharged and which is lower than the one side so that the one side is disposed to be inclined downward to the other side. a mixer in which the air and the fuel are mixed to be discharged; a turbocharging device configured to receive the mixed gas discharged from the mixer so as to compress and discharge the mixed gas; an intercooler configured to receive the mixed gas compressed in the turbocharging device so as to cool the mixed gas in a heat-exchange manner to increase in density, thereby discharging the mixed gas; a regulator configured to receive the mixed gas discharged from the intercooler so as to control an amount of mixed gas and supply the mixed gas to the engine; and an exhaust gas heat exchanger configured to heat-exchange an exhaust gas discharged from the engine with cooling water, wherein the auxiliary heat exchanger is capable of performing heat-exchange between the refrigerant and the cooling water from the engine, and wherein the exhaust gas heat exchanger has one side, through which the exhaust gas is introduced, and the other side through which the exhaust gas is discharged and which is lower than the one side so that the one side is disposed to be inclined downward to the other side.