The device serves for the cryogenic separation of air. It comprises a main heat exchanger (6) and a distillation column system for nitrogen-oxygen separation (5) with a double column (5), which contains a high-pressure column and a low-pressure column. The device also includes a mixing column (1) and means for introducing charge air via the main heat exchanger (6) into the high-pressure column and into the mixing column. A liquid oxygen line serves for introducing liquid oxygen from the low-pressure column into the upper region of the mixing column (1), an oxygen product line serves for extracting oxygen gas from the upper region of the mixing column (1) through the main heat exchanger (6). The mixing column (1) and the double column (5) are arranged in a common cold box (3). The mixing column (1) is attached to the double column (5) by way of connecting elements (10, 11).