An anastomosis assist tool comprises a body unit extending in a predetermined advancing direction, and an insertion unit arranged at the tip of the body unit. The body unit includes an anastomosis assist part having an approximately constant cross-sectional shape in a plane perpendicular to the advancing direction. The anastomosis assist part includes a projection projecting outwardly as viewed in the cross section and extending in the advancing direction. The insertion unit includes a tapered part of a diameter decreasing gradually toward a tip. When the insertion unit and a part of the body unit are inserted into a vessel, the projection of the anastomosis assist part of the body unit abuts on the inner wall of the vessel. This makes it unlikely that the inner wall of the vessel will stick to the body unit at a site other than a point abutting on the projection.
