Disclosed is a cannula that can decrease the rate of increase in resistance that is generated when penetrating an incision formed in tissue. The cylindrical cannula (1) configures a trocar (B) used during surgery； an incision member (C) can be inserted and removed therewithin； one side of the end portion of the cylinder forms a protruding slanted cut end (2)； and a tapered surface (3) having an uneven width and a width that is wider on the protruding side (the side of point 2a) of the slanted cut end than the non-protruding side (the side of point 2b) is formed on the outer periphery of the slanted cut end (2).
