The present invention relates to an injection assistance device including a body with a needle, grasping arrangement and first elastic return arrangement to dampen limited movement of the grasping arrangement, in at least one of the two directions, respectively distal or proximal, during an injection phase, and to maintain the body in its insertion position and the needle at a constant insertion length during the injection step, when the user increases, respectively releases, a distal pressure on the grasping arrangement. The invention also relates to an injection set including an injection device and the assistance device.