Abstract: An impact absorption device includes: a pair of an upper wall portion and a lower wall portion extending in the vehicle front-rear direction and placed to face each other; and a plurality of ribs extending in the vehicle front-rear direction between the upper wall portion and the lower wall portion, the ribs being arranged at predetermined intervals in the vehicle width direction so as to divide a space between the upper wall portion and the lower wall portion into a plurality of sections extending in the vehicle front-rear direction. Among the sections, three consecutive sections in an arrangement direction of the sections are configured such that an interval between ribs constituting a central section in the arrangement direction is smaller than an interval between ribs constituting each of sections adjacently placed on both sides of the central section.