Unresectable advanced gastric cancer is associated with poor prognosis. In a few studies, long-term survival was achieved with conversion surgery in patients who responded to chemotherapy. Here, we have reported a case of unresectable advanced gastric cancer in which curative resection was achieved with conversion surgery. A 70-year-old man who was diagnosed with advanced gastric cancer with multiple liver metastases received S-1/cisplatin therapy(S-1 120 mg/kg of bodyweight[bw]plus cisplatin 90 mg/kg of bw)as primary therapy. Because of the adverse reactions, secondary treatment with irinotecan therapy(CPT-11 200 mg/kg of bw)was initiated, which led to clinical complete response. A local recurrence was observed 44 months later; hence, irinotecan therapy was reinitiated. Although the disease was stable for 30 months, disseminated nodules appeared; thus, immunotherapy(nivolumab 150 mg/kg of bw)was initiated as tertiary treatment for the progressive disease. Although the number of disseminated nodules decreased, frequent blood infusions were necessary for anemia. Distal gastrectomy was planned as palliative surgery. Since no noncurative factors were detected intraoperatively, we considered that curative resection could be achieved with pancreaticoduodenectomy and changed the procedure. The operative time was 6 hours 35 minutes, and there was a blood loss of 312 g. The pathological diagnosis was ypT2- N1M0P0M0, ypStage ⅡA. At 13 months postoperatively, the patient was alive without recurrence.