A medical treatment device (12) to treat and join body tissues (L1, L2), includes at least a pair of holding members (52, 54) which is configured to hold the body tissues to be treated, an energy output portion (92, 94) provided in at least one of the pair of holding members and connected to an energy source (14) to form a joined portion (C) by supplying energy to the body tissues held by the pair of holding members to join the body tissues, and a join condition sustainment support portion (92a, 94a 162a, 164a 192a, 194a 202, 204, 206 180, 212a, 214a 224, 234 262 372a, 386a 396, 398) configured to cover an outer surface of the joined portion with a substance which prevents infiltration of the fluid to provide support so that a joined state of the body tissues is sustained.
