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.