A device for the controlled supply of a liquid within a medical flow line, includes a retaining body rotatable on an intermediate tubular connector arranged between a tubular inlet connector and a tubular outlet connector of a primary liquid and within which a bottle pierceable and containing a secondary liquid can be fitted. The retaining body includes a hollow piercing spike, rotation blocking means of the retaining body disengageable following insertion of the bottle, axial stop means of the inserted bottle, and progressive opening means of a flow passage from the hollow spike to a flow line of the primary liquid during the rotation of the retaining body with the bottle inserted therein from a first angular position of complete closure to a second angular position of complete opening.
