A device for automatic injection of a product into an injection site, said device having a longitudinal axis A and comprising: - a housing (30, 30a, 30b) receiving a container, said container being provided at one distal end with a needle and being movable relative to said housing between an initial position in which a distal end of said needle does not extend beyond a distal end of said housing and in which the container is in one of a passive state and an active state, to an insertion position, distally spaced relative to said initial position, in which said distal end of said needle extends beyond said distal end of said housing, movement of the container out of its initial position being prevented when the container is in its passive state, and being permitted when the container is in its active state, and - a safety shield coupled to and movable with respect to said housing between a first position and a second position, proximally spaced with respect to said first position, said safety shield having a free end that is distally spaced beyond a distal end of the needle when said safety shield is on said second position, movement of said safety shield from its first position to its second position placing the container in its active state, - first retaining means (61, 52) for maintaining the container in its passive state, said device being characterized in that it comprises - first deactivating means (50, 51), capable of rotating with respect to said first retaining means around said longitudinal axis A from a first position, in which said first retaining means maintain the container in its passive state, to a second position, in which said first retaining means are deactivated and allow the passage of the container in its active state, rotation around said longitudinal axis A of said first deactivating means from its first position to its second position being caused by movement of said safety shield from its first position to its second position under distal pressure exerted on said housing when a distal end of said safety shield is applied on the injection site. - a housing (30, 30a, 30b) receiving a container, said container being provided at one distal end with a needle and being movable relative to said housing between an initial position in which a distal end of said needle does not extend beyond a distal end of said housing and in which the container is in one of a passive state and an active state, to an insertion position, distally spaced relative to said initial position, in which said distal end of said needle extends beyond said distal end of said housing, movement of the container out of its initial position being prevented when the container is in its passive state, and being permitted when the container is in its active state, and - a safety shield coupled to and movable with respect to said housing between a first position and a second position, proximally spaced with respect to said first position, said safety shield having a free end that is distally spaced beyond a distal end of the needle when said safety shield is on said second position, movement of said safety shield from its first position to its second position placing the container in its active state, - first retaining means (61, 52) for maintaining the container in its passive state, said device being characterized in that it comprises - first deactivating means (50, 51), capable of rotating with respect to said first retaining means around said longitudinal axis A from a first position, in which said first retaining means maintain the container in its passive state, to a second position, in which said first retaining means are deactivated and allow the passage of the container in its active state, rotation around said longitudinal axis A of said first deactivating means from its first position to its second position being caused by movement of said safety shield from its first position to its second position under distal pressure exerted on said housing when a distal end of said safety shield is applied on the injection site.