A 74-year-old man presented to our hospital with a mass in the left supraclavicular fossa. He was diagnosed with advanced gastric cancer with liver metastasis and left supraclavicular and para-aortic lymph node metastasis, cT3N2M1 (LYM, HEP), cStage Ⅳ(the Union for International Cancer Control, TNM 7th edition). He received a total of 3 courses of S- 1 plus cisplatin therapy. Since he developed adverse reactions such as anorexia, renal dysfunction, and thrombocytopenia and the tumor was HER2-positive, he received 25 courses of capecitabine, cisplatin, and trastuzumab chemotherapy. Three years and 2 months after the first chemotherapy, remarkable tumor reduction was observed. The patient then underwent radical distal gastrectomy with D2 lymphadenectomy, and R0 resection was achieved. The histopathological diagnosis was ypT1aN0M0, ypStage ⅠA. Chemotherapy with trastuzumab may improve the long-term prognosis of HER2-positive Stage Ⅳ gastric cancer if the disease is controlled and radical resection can be achieved.