Eosinophilic gastroenteritis is a rare disease that causes various abdominal symptoms that result from the infiltration of eosinophils in the digestive tract. However, this condition has been poorly explored, and the treatment criteria and prognosis after treatment are still unclear. A 20-year-old man with a refractory duodenal ulcer had been undergoing treatment since 14 years of age at another hospital. He was admitted to our hospital with abdominal pain and anemia (hemoglobin:6.3g/dL). His blood test showed elevated serum immunoglobulin E levels, considering that he was allergic to many foods. Furthermore, endoscopic biopsy detected the occurrence of eosinophilic gastroenteritis with gastritis, duodenal ulcer, and colitis. We treated him by avoiding allergenic foods and prescribing antihistamine and vonoprazan;however, duodenal ulcer and gastrointestinal tract inflammation did not show improvement. Thus, he was diagnosed with wide-ranging and refractory eosinophilic gastroenteritis and treated with 40mg/day of steroids. After 2 months, he recovered from gastritis and duodenal ulcer, and his eosinophil level decreased, as assessed using endoscopic biopsy. Eosinophilic gastroenteritis is poorly investigated, and its treatment standards have not yet been determined. Nonetheless, steroid treatment is often applied in severe cases.