A collision avoidance support device comprising: an obstacle detection unit configured to detect an obstacle present in front of a host vehicle; an automatic brake unit (10, S14, 20) configured to cause an automatic brake, comprising a control generating a braking force in a vehicle wheel, to intervene in a case where the host vehicle is highly likely to collide with the detected obstacle; an automatic steering unit (10, S19, 30) configured to cause an automatic steering, comprising a control steering a steering wheel for collision avoidance, to intervene in a case where the host vehicle is highly likely to collide with the obstacle despite deceleration of the host vehicle by the intervention of the automatic brake; an estimation unit (S18, S42) configured to estimate whether or not the speed during the intervention of the brake representing the relative speed of the host vehicle with respect to the obstacle or representing the vehicle speed of the host vehicle at a time of the intervention of the automatic brake is higher than a speed threshold during the intervention of the brake before the intervention of the automatic steering; and an automatic steering prohibition unit (S18, S42, S44) configured to prohibit the intervention of the automatic steering based on the automatic steering unit (10, S19, 30) in a case where the estimation unit (S18, S42) estimates that the speed during the intervention of the brake is higher than the speed threshold during the intervention of the brake, characterized in that the estimation unit (SI8, S42) is configured to detect the speed during the intervention of the brake and determine whether or not the detected speed during the intervention of the brake is higher than the speed threshold during the intervention of the brake when the automatic brake intervenes. an obstacle detection unit configured to detect an obstacle present in front of a host vehicle; an automatic brake unit (10, S14, 20) configured to cause an automatic brake, comprising a control generating a braking force in a vehicle wheel, to intervene in a case where the host vehicle is highly likely to collide with the detected obstacle; an automatic steering unit (10, S19, 30) configured to cause an automatic steering, comprising a control steering a steering wheel for collision avoidance, to intervene in a case where the host vehicle is highly likely to collide with the obstacle despite deceleration of the host vehicle by the intervention of the automatic brake; an estimation unit (S18, S42) configured to estimate whether or not the speed during the intervention of the brake representing the relative speed of the host vehicle with respect to the obstacle or representing the vehicle speed of the host vehicle at a time of the intervention of the automatic brake is higher than a speed threshold during the intervention of the brake before the intervention of the automatic steering; and an automatic steering prohibition unit (S18, S42, S44) configured to prohibit the intervention of the automatic steering based on the automatic steering unit (10, S19, 30) in a case where the estimation unit (S18, S42) estimates that the speed during the intervention of the brake is higher than the speed threshold during the intervention of the brake, characterized in that the estimation unit (SI8, S42) is configured to detect the speed during the intervention of the brake and determine whether or not the detected speed during the intervention of the brake is higher than the speed threshold during the intervention of the brake when the automatic brake intervenes. <EOS>