A device for automatic injection of a product into an injection site, the product being carried by a container having an open proximal end and a substantially closed distal end and carrying a needle to provide an outlet port for the product from the container, and a piston provided in the container and movable with respect to the container, the distal movement of the piston causing the product to be expelled from the container through the needle, said device comprising: - a housing receiving at least partially said container, said container being movable with respect to said housing between an initial position, in which a tip of the needle does not extend beyond a distal end of said housing, and an insertion position, distally spaced relative to said initial position, and in which the tip of the needle extends beyond said distal end of said housing, - a safety shield coupled to said housing and movable with respect thereto between a rest position, an activation position, proximally spaced relative to said rest position, such that when the user applies the device at the injection site and pushes the housing distally, the safety shield is caused to move proximally with respect to the housing from its rest position to its activation position, and a safety position, distally spaced with respect to said rest position such that said safety shield covers said needle once the user has removed the device from the injection site, - biasing means for causing the movement of said safety shield to said safety position, - triggering means for causing the container to move from its initial position to its insertion position, said triggering means being releasable after said safety shield has moved to said activation position, - isolating means for isolating said safety shield from said biasing means when said safety shield is moved to its activation position, characterized in that said isolating means comprise a first ring, receiving said container, said first ring being coupled to said biasing means in the proximal direction and coupled to said housing in the distal direction, and being independent from said safety shield, at least when said safety shield is moved to its activation position such that the patient does not feel the force of the biasing means, and in that when the container is moved to the insertion position, said first ring is disengaged from said housing such that said first ring is coupled to said safety shield allowing said biasing means to move said safety shield to said safety position. - a housing receiving at least partially said container, said container being movable with respect to said housing between an initial position, in which a tip of the needle does not extend beyond a distal end of said housing, and an insertion position, distally spaced relative to said initial position, and in which the tip of the needle extends beyond said distal end of said housing, - a safety shield coupled to said housing and movable with respect thereto between a rest position, an activation position, proximally spaced relative to said rest position, such that when the user applies the device at the injection site and pushes the housing distally, the safety shield is caused to move proximally with respect to the housing from its rest position to its activation position, and a safety position, distally spaced with respect to said rest position such that said safety shield covers said needle once the user has removed the device from the injection site, - biasing means for causing the movement of said safety shield to said safety position, - triggering means for causing the container to move from its initial position to its insertion position, said triggering means being releasable after said safety shield has moved to said activation position, - isolating means for isolating said safety shield from said biasing means when said safety shield is moved to its activation position,