The patient was a 73-year-old man whose chief complaint was a 1-month history of anorexia and weight loss. Pyloric stenosis due to a circumferential type 2 lesion was detected on the pylorus ring from the gastric angle. Close inspection revealed a diagnosis of progressive stomach cancer cT3N+M0, stage Ⅲ. We judged that perioperative radical excision would be impossible and performed gastrojejunal bypass surgery. Postoperatively, the patient was treated with 2 courses of SOX plus trastuzumab and 7 courses of S-1. PR was identified, and a distal-side gastrectomy plus D2 lymph node dissection were performed as conversion surgery. The patient was discharged on postoperative day 9. For 1 year postoperative, no recurrence was noted. The prognosis of the unresectable gastric cancer is poor, but chemotherapy and conversion surgery in this case resulted in a favorable prognosis.