A dissecting device that includes a grasping section and a dissecting member. The grasping section has an insertion lumen that permits an imaging device to be positioned therein. The dissecting member is at the distal portion of the grasping section and is insertable into a living body and movable along a blood vessel to dissect tissue surrounding the blood vessel. The dissecting member includes a base part having a lumen that communicates with the insertion lumen and a dissecting section which extends distally from the base part. The dissecting section is configured to dissect the tissue in the living body when the dissecting member is moved along the blood vessel. The dissecting member includes a blood vessel guide passage that accepts a branch vessel branched from the blood vessel at the distal portion of the dissecting member and guides the branch vessel toward the base part.
