Tosufloxacin, which is not used to treat Mycobacterium tuberculosis, is a fluoroquinolone recommended for pneumonia when the possibility of tuberculosis infection cannot be excluded. In the present case, symptoms and chest infiltrative shadow initially improved by tosufloxacin. Therefore, we regarded this patient as having general pneumonia and did not perform follow-up chest X-ray until the infiltrates had completely disappeared. However, a few weeks later, the symptoms and the infiltrates had worsened, so M. tuberculosis was isolated from the patient's sputum. This case suggests that patients suspected of having pulmonary tuberculosis should be monitored carefully, even if antibiotics without antituberculous activity are initially effective.