An outdoor unit for a gas heat pump system, said outdoor unit comprising: a base; a compressor installed on the base; a storage tank provided at a suction-side of the compressor to store a refrigerant to be supplied to the compressor; a refrigerant pipe configured to connect the compressor to the storage tank, the refrigerant pipe being configured to guide a flow of the refrigerant; an engine which is installed on the base to provide power that drives the compressor and in which a mixed fuel of a fuel and air is burned; a cooling water pipe configured to guide a flow of cooling water that cools the engine; and a heat exchanger in which the refrigerant flowing through the refrigerant pipe is heat-exchanged, or the cooling water flowing through the cooling water pipe is heat-exchanged, characterized in that the storage tank comprises: a case in which a refrigerant storage space is defined; a partition wall disposed inside the case to partition the refrigerant storage space into an upper space and a lower space; and a gas/liquid separator provided at the suction-side of the compressor to separate a gas refrigerant of the refrigerant is defined in the upper space; a receiver configured to store a liquid refrigerant of the refrigerant is defined in the lower space, wherein the heat exchanger comprises first and second heat exchangers (150, 130), the first and second heat exchangers (150, 130) are coupled to both sides of the outer circumferential surface of the storage tank and are provided above the partition wall. a base; a compressor installed on the base; a storage tank provided at a suction-side of the compressor to store a refrigerant to be supplied to the compressor; a refrigerant pipe configured to connect the compressor to the storage tank, the refrigerant pipe being configured to guide a flow of the refrigerant; an engine which is installed on the base to provide power that drives the compressor and in which a mixed fuel of a fuel and air is burned; a cooling water pipe configured to guide a flow of cooling water that cools the engine; and a heat exchanger in which the refrigerant flowing through the refrigerant pipe is heat-exchanged, or the cooling water flowing through the cooling water pipe is heat-exchanged, characterized in that the storage tank comprises: a case in which a refrigerant storage space is defined; a partition wall disposed inside the case to partition the refrigerant storage space into an upper space and a lower space; and a gas/liquid separator provided at the suction-side of the compressor to separate a gas refrigerant of the refrigerant is defined in the upper space; a receiver configured to store a liquid refrigerant of the refrigerant is defined in the lower space, wherein the heat exchanger comprises first and second heat exchangers (150, 130), the first and second heat exchangers (150, 130) are coupled to both sides of the outer circumferential surface of the storage tank and are provided above the partition wall. a case in which a refrigerant storage space is defined; a partition wall disposed inside the case to partition the refrigerant storage space into an upper space and a lower space; and a gas/liquid separator provided at the suction-side of the compressor to separate a gas refrigerant of the refrigerant is defined in the upper space; a receiver configured to store a liquid refrigerant of the refrigerant is defined in the lower space, wherein the heat exchanger comprises first and second heat exchangers (150, 130), the first and second heat exchangers (150, 130) are coupled to both sides of the outer circumferential surface of the storage tank and are provided above the partition wall.