An air conditioner comprising: a plurality of compressors; an outlet pipe unit through which oil and/or refrigerant discharged from the plurality of compressors flows, the outlet pipe unit comprising a plurality of branch outlet pipes connected to the plurality of compressors, and a common outlet pipe receiving flows of oil and/or refrigerant from the plurality of branch outlet pipes; at least one oil separator (21-23; 80) separating oil from the oil and/or the refrigerant flowing through the outlet pipe unit; and an oil collector (40-43; 71-73; 82) collecting the oil separated by the oil separator (21-23; 80); an inlet pipe unit receiving the oil and/or refrigerant flown through the outlet pipe unit and allowing the oil and/or refrigerant to flow to the plurality of compressors, the inlet pipe unit receiving the oil separated by the oil separator (21-23; 80); a plurality of bypass pipes (51-53; 61-63; 91-93) connected to the plurality of compressors and allowing bypass flows of the oil and/or refrigerant from the plurality of compressors to the outlet pipe unit; and a pressure reduction part (34c-36c) disposed at the plurality of branch outlet pipes for reducing a pressure of oil and/or refrigerant discharged from the plurality of compressors; characterized in that the pressure reduction part (34c-36c) is formed by narrowing a portion of the plurality of branch outlet pipes to reduce cross sectional areas of the plurality of branch outlet pipes, the bypass flows of the oil and/or refrigerant of the bypass pipes (51-53; 61-63; 91-93) flow to the pressure reduction part (34c-36c), the plurality of bypass pipes (51-53; 61-63; 91-93) being connected to the pressure reduction part (34c-36c) respectively; and wherein the plurality of bypass pipes (51-53; 61-63; 91-93) are connected to the plurality of compressors at heights higher than normal oil levels of the plurality of compressors. a plurality of compressors; an outlet pipe unit through which oil and/or refrigerant discharged from the plurality of compressors flows, the outlet pipe unit comprising a plurality of branch outlet pipes connected to the plurality of compressors, and a common outlet pipe receiving flows of oil and/or refrigerant from the plurality of branch outlet pipes; at least one oil separator (21-23; 80) separating oil from the oil and/or the refrigerant flowing through the outlet pipe unit; and an oil collector (40-43; 71-73; 82) collecting the oil separated by the oil separator (21-23; 80); an inlet pipe unit receiving the oil and/or refrigerant flown through the outlet pipe unit and allowing the oil and/or refrigerant to flow to the plurality of compressors, the inlet pipe unit receiving the oil separated by the oil separator (21-23; 80); a plurality of bypass pipes (51-53; 61-63; 91-93) connected to the plurality of compressors and allowing bypass flows of the oil and/or refrigerant from the plurality of compressors to the outlet pipe unit; and a pressure reduction part (34c-36c) disposed at the plurality of branch outlet pipes for reducing a pressure of oil and/or refrigerant discharged from the plurality of compressors; characterized in that the pressure reduction part (34c-36c) is formed by narrowing a portion of the plurality of branch outlet pipes to reduce cross sectional areas of the plurality of branch outlet pipes, the bypass flows of the oil and/or refrigerant of the bypass pipes (51-53; 61-63; 91-93) flow to the pressure reduction part (34c-36c), the plurality of bypass pipes (51-53; 61-63; 91-93) being connected to the pressure reduction part (34c-36c) respectively; and wherein the plurality of bypass pipes (51-53; 61-63; 91-93) are connected to the plurality of compressors at heights higher than normal oil levels of the plurality of compressors.