Crush box and method for manufacturing same

Provided are: a crush box which is configured so that, even if the plate thickness of a cylinder body for constituting the crush box is less than 1.4 mm, the cylinder body can be satisfactorily welded to a set plate while being abutted against the set plate, and which has high axial crush performance; and a method for manufacturing the crush box. A crush box (1) has a long metallic cylinder body. The cylinder body has a flat polygonal basic cross-sectional shape surrounded by ridge line sections (2-1 to 2-4) extending in the longitudinal direction, and by side wall sections (4). The side wall sections (4) which correspond to the long sides of the cross-section and which are substantially parallel to the direction of the long axis of the cross-section have one or more groove sections (3-1, 3-2) extending in the longitudinal direction. An end of the cylinder body in the longitudinal direction has outwardly facing flanges (5-1 to 5-4).