We report a case of bulla infection caused by Mycobacterium fortuitum. The patient was a 66 year-old female associated with interstitial pneumonitis. The chest X-ray film showed cavities with thick walls and niveau formation, which initially suggested pulmonary abscesses. The chest CT scan showed infiltrative shadows surrounding multiple bullae. Smears and cultures of the sputum were repeatedly positive for mycobacteria, which was identified to be M. fortuitum. By chemotherapy with imipenem/cilastatin sodium, clarithromycin, levofloxacin, and minocycline on the basis of susceptibility test, sputum converted to negative within 2 months, abnormal shadows on the roentgenogram and laboratory data showed improvement. There are no signs of recurrence after completion of the treatment for 12 months.