A heat-pump system comprising: a first outdoor unit comprising: a first compressor, a first common suction pipe configured to guide suction of refrigerant to the first compressor, and a first oil separator; a second outdoor unit comprising: a second compressor (410, 412), a second common suction pipe configured to guide suction of refrigerant to the second compressor (410, 412), and a second oil separator; a compressor side oil balance pipe coupled to the first compressor and extended to the second outdoor unit, wherein the compressor side oil balance pipe is coupled to the second common suction pipe, wherein the compressor side oil balance pipe is configured to guide oil in the first compressor to be recovered by the second compressor; and an oil separation oil balance pipe coupled to the second oil separator and extended to the first outdoor unit, wherein the oil separation oil balance pipe is coupled to the first common suction pipe, wherein the oil separation oil balance pipe is configured to guide oil in the second oil separator to be recovered by the first compressor, characterized in that: the first outdoor unit includes a first gas-liquid separator provided at an inlet side of the first compressor, and a first gas-liquid separation oil balance pipe extended from the first gas-liquid separator to the first common suction pipe, wherein the first gas-liquid separator is configured to separate gaseous refrigerant from refrigerant and configured to supply the gaseous refrigerant to the first compressor, wherein the first common suction pipe is extending from an exit side of the first gas-liquid separator to the first compressor, wherein the first compressor is an electromotive compressor, and wherein the second compressor (410, 412) is a gas engine compressor. a first outdoor unit comprising: a first compressor, a first common suction pipe configured to guide suction of refrigerant to the first compressor, and a first oil separator; a second outdoor unit comprising: a second compressor (410, 412), a second common suction pipe configured to guide suction of refrigerant to the second compressor (410, 412), and a second oil separator; a compressor side oil balance pipe coupled to the first compressor and extended to the second outdoor unit, wherein the compressor side oil balance pipe is coupled to the second common suction pipe, wherein the compressor side oil balance pipe is configured to guide oil in the first compressor to be recovered by the second compressor; and an oil separation oil balance pipe coupled to the second oil separator and extended to the first outdoor unit, wherein the oil separation oil balance pipe is coupled to the first common suction pipe, wherein the oil separation oil balance pipe is configured to guide oil in the second oil separator to be recovered by the first compressor, characterized in that: the first outdoor unit includes a first gas-liquid separator provided at an inlet side of the first compressor, and a first gas-liquid separation oil balance pipe extended from the first gas-liquid separator to the first common suction pipe, wherein the first gas-liquid separator is configured to separate gaseous refrigerant from refrigerant and configured to supply the gaseous refrigerant to the first compressor, wherein the first common suction pipe is extending from an exit side of the first gas-liquid separator to the first compressor, wherein the first compressor is an electromotive compressor, and wherein the second compressor (410, 412) is a gas engine compressor. the first outdoor unit includes a first gas-liquid separator provided at an inlet side of the first compressor, and a first gas-liquid separation oil balance pipe extended from the first gas-liquid separator to the first common suction pipe, wherein the first gas-liquid separator is configured to separate gaseous refrigerant from refrigerant and configured to supply the gaseous refrigerant to the first compressor, wherein the first common suction pipe is extending from an exit side of the first gas-liquid separator to the first compressor, wherein the first compressor is an electromotive compressor, and wherein the second compressor (410, 412) is a gas engine compressor.