A 57-year-old man presented to the emergency department with fever and progressive altered level of consciousness of 5 days' duration. Three days before admission, influenza A was diagnosed at a clinic. On admission, his vital signs were unstable. Pneumonia was diagnosed through chest computed tomography, and urinary Legionella antigen test was positive. A diagnosis of septic shock due to Legionella and influenza pneumonia was made, and critical care management was initiated, including mechanical ventilation and vasopressors. However, tachycardia did not improve, left ventricular ejection fraction was 20%, and circulatory insufficiency progressed. Therefore, considering the involvement of septic cardiomyopathy and cardiogenic shock, veno-arterial extracorporeal membrane oxygenation (VA-ECMO) was initiated for circulation assistance on day 3 since admission. Tachycardia and myocardial dysfunction improved by day 8, and VA-ECMO was withdrawn. Subsequently, nutrition management and rehabilitation were performed, and the patient was transferred to a recovery hospital on day 108. VA-ECMO may be beneficial when concomitant with circulatory assistance in uncontrollable cases of septic cardiomyopathy using catecholamines and β-blockers. It may be necessary to adopt VA-ECMO at an appropriate time before the patient progresses to cardiopulmonary arrest.