A 67-year-old man visited hospital because of prolonged cough. Chest computed tomography (CT) revealed multiple tumors in bilateral lungs. Transbronchial lung biopsy did not reveal malignancy. Because antibiotic treatment was ineffective, partial resection of the right lung was performed for establishing the diagnosis. The pathological diagnosis was inflammatory myofibroblastic tumor. The postoperative course was uneventful. After 6 months postsurgery, he complained of breathing difficulty and exacerbation of the lesions was found by chest CT. By methylprednisolone pulse therapy, the symptom was improved, and the size of lesions reduced. Since this event, he has been administered oral prednisolone (PSL) 10 mg/day, and the exacerbation of the disease has not been noted.