A case of benign schwannoma arising in the brachial plexus with intrathoracic extension was presented. The patient was a 55-year-old man, who was pointed out an abnormal shadow in the left apical region on routine chest X-ray examination. MRI showed that the mass extended to the lowest trunk of the brachial plexus. He had no complaint. Therefore, a diagnostic operation was performed. The tumor was subcapsularly resected with thoracoscopic surgery. Histopathological examination revealed a schwannoma (Antoni type A and B). It should be kept in mind that tumors arising in the brachial plexus are a probable differential diagnosis for tumors at the pulmonary apex, even if no neurological symptoms are seen in the upper extremities.