The technical field of the invention is that of the devices used in the field of automotive safety to protect a pedestrian in the event of a frontal impact between the said pedestrian and a motor vehicle.More specifically, the invention relates to a safety device (1, 101, 201) for raising the bonnet (11, 111, 211) of a motor vehicle in the event of a collision with a pedestrian, comprising a pyrotechnic actuator (2, 102, 202, 302) provided with a thrust piston (17, 117) secured to a mechanism for raising the bonnet (11, 111, 211) and able to deploy the said mechanism which is itself secured to the said bonnet (11, 111, 211), and a blocking device intended to block the said actuator (2, 102, 202, 302) in a given position.The main characteristic of this device is that it comprises a shock-absorbing device employed when a pedestrian hits the bonnet (11, 111, 211) which has been raised, so that the assembly consisting of the bonnet (11, 111, 211), the raising mechanism and the piston (17, 117) can move under the effect of the impact while at the same time being retarded.