The present invention has been made with the aim to provide a surgical instrument, which can be put into a space between a peritoneum and muscle via a tunnel formed at the peritoneum easily and can be pulled strongly in a direction to peel the peritoneum from the muscle in hernia repair surgery or the like. A peritoneal peeling surgical instrument, which is put between muscle and a peritoneum via a tunnel formed at the peritoneum to peel the peritoneum from the muscle, includes: an operation part to be grasped and operated by the user a shaft part connected with the operation part a hinge part disposed at the tip of the shaft part and a hook part connected with the shaft part via the hinge part. In response to operation to the operation part, the hook part is bent at the hinge part with respect to the shaft part and the bending state is fixed in one or more steps. The hook part has: a convex curved surface located at a bending direction side to contact the peritoneum a flat surface located at a bending direction opposite side to contact the muscle and a streamline tip part corresponding to the tip of the hook part.
