An automatic and miniaturized injector and sample-taker device (1) for medical use comprises an enclosure (2) and at least one needle (15) movable relative to said enclosure (2). The injector and sample-taker device includes a detector system (12) suitable for detecting the presence of a blood vessel in a predetermined volume; a control unit (7) suitable for controlling the displacement of the needle as a function of information provided by said detector system (12); and at least one reservoir (13) for containing a substance for injection or to be taken.