There is provided a cannula that suppresses leakage of vitreous humor etc. from a slit through which a surgical tool is inserted. A cannula (10) used piercing through an eyeball during an ophthalmic operation, includes: a pipe (11)； a cylindrical base (12) fitted together with the circumference of a base end of the pipe (11)； a resin cap (13) including a cover surface (13c) covering the surface of the base end of the pipe (11) and a side surface (13a) covering a cylindrical side surface of the base (12)； and a slit (13d) passing through the center of the cover surface (13c). The outer diameter of the cylindrical side surface of the base (12) at a position where the cylindrical side surface of the base (12) touches the side surface (13a) of the cap is larger than the inner diameter of the side surface of the cap.
