Diabetic ketoacidosis (DKA) is a life-threatening complication of pediatric diabetes mellitus (DM). A bedside closed-loop artificial pancreas (AP) (STG-55; NIKKISO, Tokyo, Japan) maintains the blood glucose (BG) levels within the target range via automatic infusion of insulin and glucose. We report the application of the closed-loop AP to safely control the BG levels of a pediatric patient with DKA. A 12-year-old child with an unremarkable medical history presented with fever and restlessness. The patient was diagnosed with DKA secondary to fulminant type 1 DM and was treated with insulin infusion. He presented with Glasgow Coma Scale of E2V3M4. Arterial blood gas analysis revealed metabolic acidosis and BG levels of 489 mg/dL. His urine test was positive for ketones. Along with infusion therapy, automatic BG control using a closed-loop AP was initiated after ICU admission. This was adjusted to maintain BG levels within 100 mg/dL/6 h or less. After 24 h in the ICU, the patient regained consciousness and recovered from the metabolic acidosis. His general condition improved, and he was prescribed a diet treatment. The treatment was shifted to continuous insulin infusion, and he was transferred to the general ward, and was discharged on the 33rd day of hospitalization. The closed-loop AP prevented repetitive blood extractions, achieved prompt glycemic control, and prevented cerebral edema in a pediatric patient with DKA. This is the first report of successful treatment of DKA using a bedside closed-loop AP.