We report a case of IPMC complicated with obstructive pancreatitis due to perforation of the duodenum, in which radical surgery was performed. The patient was a 50-year-old man. He was referred to his previous doctor for a thorough examination of jaundice and liver damage. ERCP showed a tumour exposed in the duodenal bulb and IPMC was suspected, but biopsy showed no malignant findings. The patient was treated for obstructive pancreatitis, but the inflammatory response remained elevated. On imaging evaluation, inflammation around the pancreatic body tail remained, but inflammation around the portal vein was relatively mild. The pancreaticoduodenectomy was performed with sub-total gastric preservation. The pathology results showed a diagnosis of IPMC, with destruction of the duodenal wall due to compressible intraductal tumour growth, and a wide area of acute inflammation. The patient was treated with S-1 as adjuvant post-operative chemotherapy for 6 months and is currently recurrence-free.