Abstract: An internal organ walls joining instrument for an endoscope is used for endoscopically joining two internal organ walls spaced apart from each other, and for endoscopically forming a fistula between the two internal organ walls. The instrument has at least a first stationary part, a second stationary part, a first line member, a second line member, and a stopper. Each of the first and the second line members is respectively coupled to the first stationary part, the second stationary part, and the stopper. The two internal organ walls are pinched between the first stationary part and the second stationary. The stopper keeps the two internal organ walls in the pinched state. In this state, the fistula is made by an electro-knife. The instrument remains for a certain time until fistula becomes strong, after which it is endoscopically removed.