An interface device between external equipment and at least a venous tube for transferring fluid to a patient, the interface device having at least a first port adapted to be connected to an outlet port of the external equipment; and a venous port carried by a stator of the interface device in order to inject the fluid into the venous tube. The interface device includes a third port, the first port and the third port being carried by a movable assembly that is movable relative to the stator, the interface device being arranged to pass from any one of its configurations to another one of its configurations by the movable assembly moving relative to the stator.