A retractor holds a surgical incision in a body in an opened state to ensure a surgical field in small-incision endoscopic surgery, and includes a base body that is a thin plate made of tin having a purity of not less than 99.9% and has an elongated rectangular shape in an extended state of the base body. The retractor, in an extended form in a rectangular shape or in a rounded form in a small shape, can be inserted from a small incision wound into the body, and can easily be delivered to the surgical incision in the body by a surgical instrument. The base body is bent and deformed into a desired shape by the surgical instrument and is applied to the surgical incision in the body, so that the surgical incision can be held in an opened state so as to ensure the surgical field.