A device for automatically milking an animal, which device is provided with a milking robot, a computer for controlling the operation of the device, a measuring device (5) for performing measurements on milk obtained from an animal, at least two teat cups (1-4), and a common milk line (6) for discharging milk coming from the at least two teat cups, each teat cup (1-4) being connected via a teat cup line (7-10) to the common milk line (6). The device is provided with a milk-determining element (11-14) for determining the teat cup from which comes the milk present in the common milk line and for emitting a determination signal. The measuring device (5) comprises a common sensor for performing measurements on milk obtained from an animal and for emitting a measurement signal. The common sensor (5) is disposed in the common milk line (6). The computer is suitable for combining the measurement signal and the determination signal.