An automatic fluid injection device having an upper body (1) with an injection system (3, 4, 5) controlled by a power supply (7) and that is triggered by a user interface (100)； and an insertion mechanism (8, 9) for inserting an injection needle (110)； a base body (2) for coming into contact with an injection zone and having a fluid reservoir (6) containing an injection piston (65), and a needle assembly (10) including the injection needle (110). The injection system has an elongated spring metal strip (3) wound on a respective reel (30) before actuation； and a drive mechanism (5) for unwinding the strip (3) against a respective piston (65) so as to perform the injection, and for rewinding the strip (3) on the reel (30) after injection.
