A 55-year-old male heavy drinker was taken to another hospital because of loss of consciousness. Laboratory data showed anemia and endoscopy of the upper gastrointestinal tract disclosed intraduodenal bleeding from the ampulla of Vater. Further examinations were scheduled. However, three days later, he was given emergency admission to our hospital because of massive rectal bleeding and circulatory shock. Abdominal contrast-enhanced CT showed a pseudoaneurysm in a pseudocyst in the head of the pancreas. Emergency angiography revealed a ruptured pseudoaneurysm of the gastroduodenal artery 15 mm in diameter. He was successfully treated with transcatheter arterial embolization. ERCP demonstrated the pseudocyst communicating from the main pancreatic duct in the pancreatic head. The final diagnosis was ruptured pseudoaneurysm of the gastroduodenal artery into a pseudocyst, presenting with hemosuccus pancreaticus, secondary to chronic pancreatitis.