A 74-year-old man with poorly controlled diabetes mellitus was admitted to our hospital because of severe respiratory disturbance, fever, and sputum. We found massive consolidation of the right lung and nodular shadows on the left lung on chest X-ray, and detected influenza virus and Streptococcus pneumoniae antigen from a nasopharyngeal swab and urine sample, respectively. Co-infection with influenza virus and bacteria was suspected, and oseltamivir and biapenem were prescribed. Laboratory data improved after the addition of sivelestat sodium hydrate, an inhibitor of neutrophil-derived elastase; however, chest X-ray findings became worse on Day 8, and we administered 1 g methylprednisolone intravenously for two days. On Day 12, we detected Mycobacterium tuberculosis in the sputum, even though we did not previously detect any acid-fast bacilli, and started anti-tuberculosis drugs, such as isoniazid, rifampicin, ethambutol hydrochloride, and pyrazinamide; however, the patient died 12 days later. Severe influenza-related bacterial pneumonia with Streptococcus pneumoniae and subsequently secondary tuberculosis infection were finally suspected in this case. This was a very rare case in which additional tuberculosis infection was found in a patient with fulminant pneumonia due to co-infection of influenza virus and bacteria. It is necessary to observe patients with influenza carefully, especially when steroids are used, even if antibiotics are also administered.