A socket is adapted for being disposed in a sleeve hole of a wrench wherein the sleeve hole has a positioning element disposed on an inner wall of the sleeve hole. The socket includes a main body having a driving portion and a connecting portion at two ends. The connecting portion has a polygonal external surface including plural driven faces arranged around an axial direction. A shared edge is formed between every two adjacent driven faces, and at least one shared edge is formed with a notch for receiving the positioning element. The notch has a triangle cross-section and has a steeper first bottom face and a second bottom face which is more remote from the driving portion than the first bottom face. Thus, the socket can be prevented from moving forward and is easier to remove.