A 68-year-old man who underwent cholecystectomy for acute cholecystitis and was diagnosed with gallbladder duct carcinoma was referred to our hospital. Postoperative computed tomography showed thickening of the middle to lower bile duct without any tumorous lesions. Endoscopic retrograde cholangiopancreatography and intraductal ultrasonography revealed irregular wall thickening of the lower bile duct and apparent infiltration of gallbladder duct tumor to the common bile duct without pancreaticobiliary maljunction. Subtotal stomach-preserving pancreaticoduodenectomy was performed. Pathological examination showed papillary adenocarcinoma and tubular adenocarcinoma in the gallbladder duct and BilIN-3 lesion in the distal bile duct. The final diagnosis was biliary simultaneous multicentric cancer without pancreaticobiliary maljunction.