A treatment device is disclosed, which includes a dissecting section main body which is configured to dissect tissue in a living body when inserted into the living body along a blood vessel, and which has a slit permitting a branch vessel branched from the blood vessel to enter into the slit, a stanching section which is disposed at the slit and which presses and cauterizes the branch vessel introduced into the slit, and a cutting section which is disposed at the slit and which cuts the cauterized branch vessel.
