The case was a 56-year-old man. A nodular shadow of the left upper lobe was found in the chest computed tomography, and a diagnosis of adenocarcinoma was obtained by bronchoscopy. Preoperative 3-dimensional computed tomography (3D-CT) angiography indicated an extremely rare pulmonary artery bifurcation abnormality in which A4b+5 and A8+9 bifurcate from the left main pulmonary artery. Thoracoscopic left upper lobectomy and lymph node dissection were performed. Pathological diagnosis was adenocarcinoma with pStage I B. The mediastinal basal pulmonary artery is extremely rare, and to our knowledge, the bifurcation pattern of this case has not been reported elsewhere. The 3D-CT angiography was useful to detect the anatomical vascular abnormalities of the pulmonary artery before surgery, for the safe performance of the thoracoscopic surgery.