A 61-year-old man was referred to the urology department in our hospital with gross hematuria and hydro nephrosis. Cystoscopy revealed a smooth mass lesion in his bladder, and a transurethral biopsy was performed. Signet ring cell carcinoma was found in the submucosa. Upper gastrointestinal endoscopy revealed an ulcerated lesion in his gastric body. Biopsy specimens obtained from the ulcerated lesion showed signet ring cell carcinoma. No other primary lesions were detected using colonoscopy, gallium scintigraphy, or computed tomography of the chest. He was ultimately diagnosed with advanced gastric cancer with bladder metastasis. He was prescribed combination chemotherapy of cisplatin and tegafur, gimeracil, oteracil potassium, and trastuzumab. After 2 courses of chemotherapy, there was a decrease in the size of both the gastric and bladder lesions. There was also a significant decrease in the tumor marker levels. He is currently alive after 7 courses of chemotherapy.