A cascade unit is a cascade unit of a refrigeration system including a first circuit, a second circuit, and a cascade heat exchanger. The first circuit includes a first connecting portion that connects a first pipe and a second pipe extending from the cascade heat exchanger, of the first pipe and the second pipe connecting a first heat exchanger and the cascade heat exchanger), to the first pipe and the second pipe extending from the first heat exchanger inside or outside a cascade casing. The second circuit includes a second connecting portion that connects a liquid pipe and gas pipes extending from the cascade heat exchanger, among the liquid pipe and the gas pipes connecting second heat exchangers and the cascade heat exchanger, to the liquid pipe and the gas pipes extending from the second heat exchangers inside or outside the cascade casing.

Provided is an air conditioner which comprises multiple outdoor units, the air conditioner being configured so that, with the use of a low cost configuration, required refrigeration machine oil is supplied to all the outdoor units through refrigerant piping and so that the air conditioner has increased reliability. An air conditioner is provided with multiple indoor units and with four outdoor units which are connected to the multiple indoor units through refrigerant piping. A line of first refrigerant piping leading from the multiple indoor units is branched into two lines of second refrigerant piping, each of the two lines of second refrigerant piping is branched into two lines of third refrigerant piping, and the four lines of third refrigerant piping are respectively connected to the four outdoor units.

Provided is an air conditioner which comprises multiple outdoor units, the air conditioner being configured so that, with the use of a low cost configuration, required refrigeration machine oil is supplied to all the outdoor units through refrigerant piping and so that the air conditioner has increased reliability. An air conditioner is provided with multiple indoor units and with four outdoor units which are connected to the multiple indoor units through refrigerant piping. A line of first refrigerant piping leading from the multiple indoor units is branched into two lines of second refrigerant piping, each of the two lines of second refrigerant piping is branched into two lines of third refrigerant piping, and the four lines of third refrigerant piping are respectively connected to the four outdoor units.