A 66-year-old man complaining of fever was given intravenous antibiotic therapy, but he did not improve. After subsequent admission, chest X-ray film and computed tomography scans showed large bullae and consolidation in the right lung field. A transbronchial lung biopsy specimen revealed infiltration of mononuclear cells in alveolar septa and organizing lesions in alveolar ducts. We considered this case to be cryptogenic organizing pneumonia (COP) from its clinical course and pathological findings. Treatment with corticosteroid resulted in disappearance of the large bullae and consolidations. COP accompanied by large bullae is very rare. The large bullae may have been caused by check-valve mechanism.