An apparatus (100) for collecting blood samples comprises a sleeve (1) having a substantially cylindrical body (10), hollow on the inside, defining an inner chamber (11) open at the front and rear, a needle assembly (5) comprising a needle-carrier (50) which carries at its opposite ends a first external needle (51) designed to be inserted into the patient's vein and a second internal needle (52) designed to engage in a vacutainer-type test tube, and a safety device (7) having a substantially cylindrical hollow body (70) defining an inner chamber (71) able to receive the vacutainer-type test tube. The safety device is able to support the needle assembly (5) so that the internal needle (52) is disposed axially inside the chamber (71) of the safety device and the safety device (7) is mounted movably inside the chamber (11) of the sleeve (1) to pass from a working position in which the external needle (51) protrudes axially outward from the sleeve (1) to a safe position in which the external needle (51) is protected inside the chamber (11) of the sleeve (1) and the internal needle (52) is protected inside the chamber (71) of the safety device (7).