A 61-year-old woman was referred to our hospital for a double balloon endoscopy (DBE) examination of small intestine. She had undergone laparotomy for a perforated ulcer of the 3rd portion in the duodenum 3 years prior to this admission. Esophagogastroduodenoscopy at the previous hospital revealed multiple ulcers in the 2nd and 3rd portions in the duodenum. DBE revealed multiple ulcer scars in the proximal jejunum. Zollinger-Ellison syndrome was suspected from the distribution of the ulcers and scars. Serum gastrin was high and a selective arterial calcium injection test showed a step up of gastrin level only in the gastroduodenal artery area. We diagnosed a gastrinoma located on the ventral side of the 2nd portion of the duodenum from imaging studies. The tumor was extirpated and histologically found to be a neuroendocrine tumor in a lymph node. Serum gastrin level decreased to the normal range a day after surgery.