A 70-year-old man was referred to our hospital after anemia was identified by his general practitioner. A detailed examination led to the diagnosis of unresectable StageIV gastric cancer with metastasis to the paraaortic lymph nodes. The cancer was HER2-positive; therefore, the patient was administered trastuzumab, capecitabine, and cisplatin combination therapy. A remarkable reduction in the size of the lymph nodes was observed. The reduction in the size of the metastatic foci was accompanied by enlargement of the primary tumor, which was considered an indication for surgery. He underwent total gastrectomy, and histopathology showed absence of cancerous cells in the resected lymph nodes, indicating a curative resection. In Japan, trastuzumab, capecitabine, and cisplatin combination therapy is currently recommended as the standard therapy for unresectable advanced/recurrent HER2-positive gastric cancer, and the findings of the present case suggest that it may also be useful as neoadjuvant chemotherapy.