If smooth transportation of bile toward the duodenum is difficult due to cancerous cells growing in the bile duct or due to stricture of the bile duct, a cylindrical stent may be implanted into the stenosed site of the bile duct to enable smooth supply of bile. Conventional stents have no risk of slippage at an implanted position thereof, but suffer from invasively growing cancerous cells. Although a covered stent having a coating has been proposed to solve invasion of the growing cancerous cells, the covered stent may have a risk of slippage at an implanted position thereof and also, may cause pancreatitis and cholelithiasis. To solve the above described problems, disclosed herein is a stent to prevent backflow of food from the duodenum to the bile duct while assuring smooth transportation of bile without a risk of unwanted displacement caused by the transported bile. The stent includes a cylindrical outer stent, and a downwardly tapered inner stent covered with a polytetrafluoroethylene (PTFE) or silicone coating having biocompatibility. The inner and outer stents are coupled to each other to define a double structure.