Abstract: This invention relates to a reinforcement member to be mounted internally in the doors of an automobile, and more particularly to the member comprising two parallel flat members and one or two corrugated members which connect said two parallel members in such a manner as to position the ridges of folds thereof perpendicular to the surfaces of the plate members. The reinforcement member is mounted internally in car doors. When the car receives an impact from the side of the door, the corrugated surfaces of the member can distribute the impact evenly by deforming themselves into a fan-like shape to thereby prevent the door from being abruptly folded at one point.