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 , the first and second heat exchangers 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 , the first and second heat exchangers 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 , the first and second heat exchangers are coupled to both sides of the outer circumferential surface of the storage tank and are provided above the partition wall . <EOS>