We report a 45-year-old man with type 2 diabetes who presented with recurrent hypoglycemia. Biochemical and imagingstudies did not show any mass-like lesion in the pancreas, so prednisolone and diazoxide were administered for the treatment of hypoglycemia. However, the hypoglycemia persisted during and after the medical treatment. A selective arterial calcium stimulation test was performed and revealed a suspicious lesion at the head of the pancreas. The patient underwent enucleation of the pancreas head lesion. The lesion was confirmed histologically to be focal nesidioblastosis and surgical resection was successfully performed. The patient showed no hypoglycemic symptoms postoperatively.