A 50-year-old man showed massive lower gastrointestinal bleeding without a triggering episode. An emergency colonoscopy revealed a protruding vessel in the lower rectum with no active bleeding. No underlying ulcer was seen within the surrounding mucosa. These findings were consistent with rectal Dieulafoy's lesion. Angiography was requested to identify the source of bleeding and for possible embolization. On the initial angiography, the bleeding point was unclear. Abnormal vessels such as arteriovenous malformation or nidus were not found. He again developed hematochezia, requiring transfusion of red blood cells. However, the second colonoscopy showed no active bleeding from the protruding vessel in the rectum. During the second angiography, sudden bleeding occurred. Angiography showed extravasation of contrast medium from the distal branch of the superior rectal artery. Transcatheter arterial embolization was performed, and was very effective.