A fistulectomy method of forming a fistula between a first duct and a second duct is provided. The method including: inserting an insertion portion of an endoscope having a channel into the first duct； inserting a treatment instrument into the channel； feeding a distal end of the treatment instrument into the second duct through the first duct； discharging a first magnet from the distal end of the treatment instrument to the second duct； pulling the treatment instrument from the second duct； discharging a second magnet to the first duct； and attaching the first magnet and the second magnet magnetically when the first and second ducts are between the first and second magnets.
