A medical device for fusing or necrosing a biological tissue, including a first electrode member and a second electrode member protruded from a non-electrically-conductive attachment portion configured to sandwich the biological tissue; and an energy supply unit configured to supply electric energy to between the first electrode member and the second electrode member, wherein the region of a predetermined length in a direction of axial line from the attachment portion in at least one of the electrode members within the first electrode member and the second electrode member is coated with an electrical insulator.