A method for dissecting a submucosal layer includes: incising at a tissue portion surrounding an area including a lesion in a gastrointestinal tract； fixing a thread first end to the area including the lesion, the suture thread including a second end having a needle, and barbs arranged along a longitudinal axis between the first and second ends； piercing the needle to a tract wall that faces the area including the lesion and pulls the thread through the tract wall into the gastrointestinal tract； holding a state of lifting at least a portion of the area including the lesion by pulling the needle or the thread, lifting a tract wall at least the portion including the lesion, and engaging the barbs with the tract wall； dissecting the submucosal layer of the gastrointestinal tract in the state of lifting at least the portion of the area including the lesion.
