A 44-year-old man presented to our hospital with a 1-day history of progressively worsening abdominal pain. He had eaten a heavy meal the previous night. Abdominal computed tomography showed a large amount of intra-abdominal fluid and extravasation of contrast medium from an artery of the greater omentum in the left upper abdomen. The patient was diagnosed as having intra-abdominal hemorrhage caused by bleeding from the greater omentum and emergency operation was performed. Since the patient was hemodynamically stable and the site of bleeding was confirmed, laparoscopic surgery was performed. Intraoperative examination revealed bleeding from the omental branch of the left gastroepiploic artery, and partial resection of the omentum including the left gastroepiploic vessels was performed. The postoperative course was uneventful, and the patient was discharged on the 6th postoperative day. Histopathological examination of the resected specimen showed no abnormal findings, such as neoplasms and aneurysms. Based on histopathological findings and absence of a history of trauma, the final diagnosis was idiopathic omental bleeding.