A 79-year-old male patient was referred to our healthcare facility because of an abnormal CT shadow detected during follow-up of prostatectomy. The nodules revealed a tendency of increasing in size, and primary lung cancer was suspected. The patient underwent a right lower lobectomy and mediastinal lymphadenectomy via video-assisted thoracic surgery. As there was no evidence of primary disease in other organs, we diagnosed the patient with primary malignant melanoma of the lungs (PMML). Postoperative pathological examination revealed no lymph node metastasis. However, bronchoscopy revealed slight brownish-toned changes in the resection margins of the right lower lobe of the bronchus. Biopsies of the resected margins confirmed the presence of malignant melanoma cells. Owing to the presence of BRAF mutated cells in the surgical specimen, dabrafenib/trametinib treatment was initiated. Subsequent bronchoscopy revealed new brownish-toned changes in the bronchial mucosa from the trachea to the right bronchus, suggesting malignant melanoma. The patient underwent regular bronchoscopic examinations from that time with no major deterioration and is still undergoing treatment. Although PMML has a poor prognosis, in this case, disease control was achieved over a long period through molecular targeted therapy for the BRAF mutation, and bronchoscopy was useful in determining the therapeutic effects.