A 65-year-old male was diagnosed to have diffuse dilation of the main pancreatic duct (MPD) on US. EUS revealed a wall irregularity of the MPD only in the head of the pancreas. Duodenoscopic finding was a swollen major papilla with production of mucin from a dilated orifice. A balloon-occluded ERP showed defects only in the ducts of Wirsung and Santorini in the pancreatic head. Peroral pancreatoscopy (POPS) showed a papillary tumor with redness. Intraductal ultrasonography (IDUS) showed an intraductal echogenic area with fine reticular pattern (FRP) only in the pancreatic head and 3 layers of the pancreatic duct with external FRP in the distal portions. We made a diagnosis of main duct type mucin-producing tumor of the pancreas localized in the pancreatic head with no parenchymal involvement. Pancreatoduodenectomy was performed and the pathological examination revealed adenoma.