Patients who have been diagnosed as having acute pancreatitis should be, on principle, hospitalized. Crucial fundamental management is required soon after a diagnosis of acute pancreatitis has been made and includes monitoring of the conscious state, the respiratory and cardiovascular system, the urinary output, adequate fluid replacement and pain control. Along with such management, etiologic diagnosis and severity assessment should be conducted. Patients with a diagnosis of severe acute pancreatitis should be transferred to a medical facility where intensive respiratory and cardiovascular management as well as interventional treatment, blood purification therapy and nutritional support are available. The disease condition in acute pancreatitis changes every moment and even symptoms that are mild at the time of diagnosis may become severe later. Therefore, severity assessment should be conducted repeatedly at least within 48 h following diagnosis. An adequate dose of fluid replacement is essential to stabilize cardiovascular dynamics and the dose should be adjusted while assessing circulatory dynamics constantly. A large dose of fluid replacement is usually required in patients with severe acute pancreatitis. Prophylactic antibiotic administration is recommended to prevent infectious complications in patients with severe acute pancreatitis. Although the efficacy of intravenous administration of protease inhibitors is still a matter of controversy, there is a consensus in Japan that a large dose of a synthetic protease inhibitor should be given to patients with severe acute pancreatitis in order to prevent organ failure and other complications. Enteral feeding is superior to parenteral nutrition when it comes to the nutritional support of patients with severe acute pancreatitis. The JPN Guidelines recommend, as optional continuous regional arterial infusion and blood purification therapy.