A 78-year-old male was referred to our hospital for abnormal findings on a chest radiograph. A chest CT showed two tumors in the left upper lobe and a tumor in the right lower lobe, and each tumor had a different characteristic. Positron emission tomography-CT suggested that all of these tumors were malignant, and the hilar and mediastinal lymph node metastasis and distant metastasis were not detected. One tumor was diagnosed by bronchoscopy as adenocarcinoma. The patient underwent left upper lobectomy and partial resection of the right lower lobe. The tumors in the left S¹⁺²b and left S¹⁺²c were adenocarcinoma and large cell carcinoma, respectively, and the right S⁶ tumor was squamous cell carcinoma. We diagnosed that these tumors were synchronous triple lung cancers. He is now under observation without recurrence for 1 year. When lung cancer with multiple tumors is diagnosed, the possibility of synchronous multiple lung cancers should be taken into consideration to not miss a need for surgery.