the impact to vanish see fig6 a that is if a collision impact is transferred to the bumper back beam 1 the support member 300 slides into the buffer member 200 in a state that the support member 300 is pressingly fixed by the pressingly fixing portions 220 of the buffer member 200 to absorb the impact and thus the impact of the bumper back beam 1 is prevented from being transferred to the side member 2 see fig6 b as described above the impact being transferred to the bumper back beam 1 when a low speed vehicle collision occurs is absorbed through the bumper stay structure 1000 and thus passengers can be safely protected on the other hand as illustrated in fig7 a to 7c if a vehicle collision occurs during a high speed driving of the vehicle impact is transferred to the bumper back beam 1 through the bumper and then transferred to the bumper stay structure 1000 that supports the bumper back beam 1 that is if a collision impact is transferred to the bumper back beam 1 the support member 300 slides into the buffer member 200 in a state that the support member 300 is pressingly fixed by the pressingly fixing portions 220 of the buffer member 200 to firstly absorb the impact and thus the impact of the bumper back beam 1 is firstly prevented from being transferred to the side member 2 see fig7 a then the guide protrusions 310 formed at the front end of the support member 300 slide into the side member 2 as they are coupled to the guide grooves 120 formed on the plate 100 see fig7 b then the deforming portions 210 of the buffer member 200 are buckled by the collision impact.