A refrigeration cycle system, using a second coolant and a second lubricating oil in place of a first coolant and a first lubricating oil used previously in the refrigeration cycle system wherein an outdoor unit has been replaced the replacement outdoor unit comprising newly employed components which use the second coolant, said system comprising: the replacement outdoor unit including a compressor, and a heat-source-unit-side heat exchanger; an indoor unit including a user-side heat exchanger; a first pipe interconnecting one end of the outdoor unit to one end of the indoor unit; a second pipe interconnecting the other end of the indoor unit to the other end of the outdoor unit; wherein, the refrigeration cycle system further includes a storage apparatus situated within the coolant flow path for consecutively storing the first lubricating oil remaining in said first and second pipes and/or said indoor unit while ordinary air conditioning/cooling operation is performed, wherein the first lubricating oil has a lower density than the second coolant and the second lubricating oil, characterised in that the storage apparatus comprises an isolation region and a storage region divided by means of a partition plate which extends from the bottom of the storage apparatus to a certain height, the partition plate for capturing the first lubricating oil within the storage region by means of the inlet pipework into the storage apparatus being located through a sidewall of the storage apparatus into the isolation region and wherein the top of the partition plate is higher than an inlet position of the second coolant, and wherein the outflow pipe extends from the lower side of the isolation region, thus separating and storing the first lubricating oil in the storage region. the replacement outdoor unit including a compressor, and a heat-source-unit-side heat exchanger; an indoor unit including a user-side heat exchanger; a first pipe interconnecting one end of the outdoor unit to one end of the indoor unit; a second pipe interconnecting the other end of the indoor unit to the other end of the outdoor unit; wherein, the refrigeration cycle system further includes a storage apparatus situated within the coolant flow path for consecutively storing the first lubricating oil remaining in said first and second pipes and/or said indoor unit while ordinary air conditioning/cooling operation is performed, wherein the first lubricating oil has a lower density than the second coolant and the second lubricating oil, characterised in that the storage apparatus comprises an isolation region and a storage region divided by means of a partition plate which extends from the bottom of the storage apparatus to a certain height, the partition plate for capturing the first lubricating oil within the storage region by means of the inlet pipework into the storage apparatus being located through a sidewall of the storage apparatus into the isolation region and wherein the top of the partition plate is higher than an inlet position of the second coolant, and wherein the outflow pipe extends from the lower side of the isolation region, thus separating and storing the first lubricating oil in the storage region.