A 68-year-old Japanese man was admitted to our hospital complaining of a one-month history of dyspnea and dry cough. He had eruptions on his face and extremities and severe acute respiratory failure. On laboratory tests, ferritin and KL-6 levels were high, and antibodies to anti-aminoacyl-tRNA synthetase (anti-PL-7 antibody) were present. Chest computed tomography showed ground-glass opacities in both lower lobes with volume loss and traction bronchiectasis, and a mass in the right lower lobe. Anti-PL-7 antibody-positive dermatomyositis–rapidly progressive interstitial pneumonia and lung cancer were diagnosed. The pulmonary infiltration seen on chest X-ray improved gradually after intensive therapy consisting of noninvasive positive pressure ventilation, pulse methylprednisolone, pulse cyclophosphamide, and cyclosporine A. After confirming that his respiratory status was stable, transbronchial biopsy was performed, and squamous cell lung cancer cT4N0M0 Stage III A was diagnosed. Anti-cancer drug treatment resulted not only in tumor shrinkage, but also in improvement of ground-glass opacities, the serum ferritin level, and pulmonary function. This case suggests that treatment of lung cancer with anti-aminoacyl-tRNA synthetase (anti-PL-7 antibody)-positive dermatomyositis–interstitial pneumonia is effective for control of interstitial pneumonia.