A vaginal wall incision instrument includes a main body portion that is capable of being inserted into a vaginal canal; an incision portion that protrudes from a distal portion of the main body portion in a direction intersecting a center line of the vaginal canal and is formed by a conductive material; and an operating portion, wherein the main body portion includes an exterior portion and an interior portion, wherein the interior portion includes a contact portion, wherein a guide hole is configured on the interior portion, wherein the guide hole is capable of guiding the conductive member in a direction toward a boundary between the uterine cervix and the vaginal canal, and wherein the incision portion separates the vaginal canal along a circumference whose center is the center line of rotation by rotating the interior portion about the center line of rotation with respect to the exterior portion.