A crush box arranged between a side member of a vehicle body and a bumper reinforcement member, the crush box including: a main body portion arranged in a longitudinal direction of a vehicle and formed in a tubular shape, the main body portion having first and second portions; a vehicle body attaching portion arranged at a first end of the main body portion; and a bumper attaching portion arranged at a second end of the main body portion, wherein vertical cross-sections of both the first portion adjacent to the vehicle body attaching portion and the second portion adjacent to the bumper attaching portion are polygonal shapes, and the number of vertices of the polygonal shape of the vertical cross-section of the second portion is greater than the number of vertices of the polygonal shape of the vertical cross-section of the first portion.