A 43-year-old woman was referred to our hospital for an abnormal shadow on chest X-ray. Computed tomography revealed a tumor with calcification of 9.8 cm in size at the anterior mediastinum. The infiltration into the left brachiocephalic vein and superior vena cava by tumor was suspected. Surgery was performed under a diagnosis of mature teratoma. The tumor was found to adhere firmly to superior vena cava (SVC), left brachiocephalic vein, right phrenic nerve, and the arch of the azygos vein. To ensure the blood flow, an artificial blood vessel was placed between left brachiocephalic vein and right atrium. Then SVC was clamped and the tumor was resected with the part of SVC.