If surgical treatment is not possible in patients with malignant obstruction in the common bile duct, placing metal stents using endoscopy is a standardized treatment to resolve biliary obstruction. The metal stent is located in the bile duct to cover the stenotic portion by malignant tumors. The lower end of the metal stent can be located inside the common bile duct above the major ampulla or in the duodenum through the major ampulla. These two procedures with supra- or trans-papillary stents are currently being performed in general clinical practices, depending on the preference of the endoscopists. Until now, the comparison of the clinical results of the two procedures has been scarcely studied, and there is no prospective study yet. Therefore, researchers aim to compare the clinical results of two stent procedures through prospective randomized controlled studies.