A patient with insulinoma diagnosed by clinical features and localized preoperatively using a combination of contrast-enhanced ultrasonography (CEUS), dual phase contrast enhanced spiral computed tomography (DPSCT) and arterial stimulation and venous sampling (ASVS) was reported. A 37-year-old man was admitted to our hospital because of hypoglycemic attacks, palpitations, and muscular weakness. Fajans' ratio reported to be an index for insulinoma was positive. Transabdominal computed tomography and ultrasonography failed to detect any abnormalities. CEUS showed a small low echoic lesion in the pancreatic body with blood flow and the early arterial phase of DPSCT revealed a small strengthening focus, which mimicked a pancreatic tumor in the pancreatic body. ASVS showed that the insulin levels in the hepatic vein were extremely increased by calcium injection to the gastroduodenal artery. An open intra-abdominal operation was performed and an insulinoma was confirmed in the pancreatic body. Enucleation of tumor was undertaken and histopathological examination showed an adenoma, insulin expression was positive in immunofluorescence staining. Symptomatic hypoglycemia never happened even without glucose infusion since the operation. His blood glucose level improved to within the normal range.