The patient was a 63-year-old woman with a history of diabetes. At initial diagnosis, blood tests suggested the presence of severe infection because the while cell count was 20800/μl and the C-reactive protein level was 35.6 mg/dl, but computed tomographic(CT)imaging showed no gas in the submandibular space. She received anti-inflammatory treatment after hospitalization, but the symptoms did not improve. We therefore repeated CT imaging and discovered gas in the tissue space around the submental region. Based on the diagnosis of cervical necrotizing fasciitis, we performed emergency surgery, curettage of the lesion, and open surgery. The preoperative plain chest X-ray films the showed no abnormal findings. On the following day after surgery, SpO2 fell to the range of 80 %. A plain chest X-ray film showed shadows over the entire right lung field. The left lung showed signs of pneumonia with diffuse shadows. Chest CT images revealed shadows and accumulations of pleural effusion in both lung fields. The patient was given a diagnosis of a lung injury due to acute respiratory distress syndrome(ARDS)complicated by a severe infection. She received an intravenous drip infusion of sivelestat sodium (product name: Elaspol R)at a dose of 200 mg/day for 7 days. Pneumonia started to improve on the day after starting treatment. Our findings suggest that patients with severe infection should receive systemic management, bearing in mind potential complications of ARDS.