A medical treatment device to treat and join body tissues, includes at least a pair of holding members which is configured to hold the body tissues to be treated, an energy output portion provided on at least one of the pair of holding members and connected to an energy source to form a joined portion by supplying energy to the body tissues held by the pair of holding members to join the body tissues, and a join condition maintenance assistance portion capable of applying a substance which prevents infiltration of the fluid to the body tissues to be treated to provide assistance so that a joined state of the body tissues is maintained.