The present invention relates to an injection assistance device (1) comprising a body (2) with a needle (7), grasping means (4) and first elastic return means (9) to dampen limited movement of said grasping means (4), in at least one of the two directions, respectively distal or proximal, during an injection phase, and to maintain said body (2) in its insertion position and said needle (7) at a constant insertion length during the injection step, when the user increases, respectively releases, a distal pressure on the grasping means (4).The invention also relates to an injection set (100) comprising an injection device (3) and the said assistance device (1).