A 62-years-old Japanese male, who had mediastinal tumor at the left thoracic inlet, was admitted to our hospital to receive surgical treatment. The tumor behind the left subclavian artery was guessed to be neurogenic benign tumor, though the involvement of the brachial plexus was unclear. We approached the tumor by means of left hemi-collar skin incision, resulting in performing safe operation with directly looking at the tumor that communicated with 1st intercostal nerve and inferior trunk of the left brachial plexus. Pathological diagnosis of the resected tumor was ganglioneuroma. Cervical approach by means of hemi-collar skin incision is thought to be available for surgical treatment of tumors at the thoracic inlet because of easy accessibility and less invasiveness than other approach with dividing bones, such as clavicle, sternum, or ribs.