A 64-year-old woman with complete atrioventricular block caused by sarcoidosis was emergently placed a pacemaker. A 10 mm nodule in the left upper lobe of the lung and the mediastinal and bilateral hilar lymphadenopathy was detected through chest computed tomography. To establish the diagnosis, resection of the tumor and #4L was performed. By intraoperative pathology, the nodule was diagnosed as an adenocarcinoma and #4L was found to be a granuloma without metastasis of carcinoma. Subsequently, left upper lobectomy and lymph node dissection (ND2a-2) was conducted. Pathological stage was stageⅠA1 lung cancer. No recurrence has been noted for a year postoperatively and lymphadenopathy has improved by administering prednisolone medication.