In the case of a transconjunctival single-plane sclerocorneal incision, when a surgeon pushes a blade portion forward from near a limbus toward an anterior chamber via conjunctiva, sclera, and cornea along a substantially S-shaped movement path, a rotation moment easily occurs in a direction such that the proximal end of the blade portion is pushed up and also the front end of the blade portion is pushed down. For this reason, it is easy for the surgeon to push the blade portion forward along a movement path in a perforation direction into the anterior chamber via a movement path in an advancing direction from the sclera to cornea. A substantially S-shaped incisional wound with good self-closing property can be easily formed. When the blade portion advances to the anterior chamber, the blade portion linearly advances along a movement path in a direction in which the blade portion is not translated downwardly, and the inner incision line of the incision wound is not likely to have the shape of an inverted "V".
