A shock absorber has a first and second end surfaces opposite to each other in an axial direction, and a plurality of connection surfaces. The first end surface is an N-sided polygon (N is an integer of 3 or more), and the second end surface is an M-sided polygon (M is an integer of 4 or more and more than N). (MN) vertices are provided at intermediate positions in the axial direction on a circumferential surface defined by the plurality of connection surfaces. From the vertices, one first ridgeline reaches one vertex of the first end surface and two second ridgelines reach a corresponding one of two vertices of the second end surface. The remaining vertices are connected to each other by (2NM) third ridgelines. The first ridgeline, the second ridgelines, and the third ridgelines define the plurality of connection surfaces.