A device (1) for the injection of a product at an injection site, the product being carried by a container (2) having an open proximal end (2a) and a substantially closed distal end (2b) carrying a needle (4 ) to provide an outlet for the product from the container, and a piston (5) disposed in the container and which can move relative to the container, making the movement of the piston that the product is ejected from the container through the needle , said device (1) comprising: - a housing (15) receiving at least partially said container (2), said container (2) being able to move relative to said housing (15) between an initial position, in which a tip of the needle (4) does not extend beyond a distal end (15b) of said housing (15) and an insertion position, distally separated in relation to said initial position, and in which the tip of the needle (4 ) extends beyond said distal end (15b) of said housing (15), - a needle guard (6) releasably coupled with said container (2), to protect said needle (4) before the use of the device (1), said device being (1) characterized in that it further comprises: - retention means (13, 14, 17) arranged at or near said distal end (2b) of said device (1), designed to prevent said container (2) from moving distally with respect to said housing (15) until said needle guard (6) is removed from said container (2), - said retaining means comprising at least one flexible element (13), said flexible element being able to deflect from a tensioned position, in which said flexible element prevents said container (2) from moving distally with respect to said housing (15), to a released position, in which said flexible element (13) does not prevent said container (2) move distally with respect to said housing (15), making the removing said needle guard (6) from said container (2) that said flexible element (13) passes from its tensioned position to its released position, - said needle protector (6) comprising a pushing surface (9), being sa
