Device for the controlled supply of a liquid within a medical flow line, comprising a retaining body (7) rotatable on an intermediate tubular connector (4) arranged between a tubular inlet connector (2) and a tubular outlet connector (3) of a primary liquid and within which a bottle (F) pierceable and containing a secondary liquid can be fitted. The retaining body (7) comprises a hollow piercing spike (11), and provided for are rotation blocking means (17, 18) of the retaining body (7) disengageable following insertion of the bottle (F), axial stop means (12, 29) of the inserted bottle (F), and progressive opening means (20, 23) of the flow passage from the hollow spike (11) to the flow line of the primary liquid during the rotation of the retaining body (7) with the bottle (F) inserted therein from a first angular position of complete closure to a second angular position of complete opening.
