A retractor is provided that can form a joint cavity internal space for a field of view for an endoscope and practice of a treatment in a state where a wound area is spread. A retractor includes first arm portions 2 and 3 and a second arm portion 4 positioned between the first arm portions 2 and 3. The first arm portions 2 and 3 include first claw portions 12 and 13 to be hung on a wound area entrance edge. The second arm portion 4 includes a second claw portion 14 to be hung on the wound area entrance edge. When the first arm portions 2 and 3 and the second arm portion 4 are in a closed state, the first claw portions 12 and 13 and the second claw portion 14 overlap with each other.