A 70-year-old man was found to have a moderately differentiated squamous cell carcinoma in the mid-esophagus on X-ray and endoscopy. These examinations revealed no lesion in the stomach at that time. Ten days after termination of preoperative hyperthermo-chemo-radiotherapy (HCR), a subtotal esophagectomy and gastric tube reconstruction via the retrosternal route were performed (pTNM stage I). Seven months later, another early cancer was detected in the reconstructed gastric tube. Via a median sternotomy, a wedge resection of the gastric tube was performed, and histopathological studies revealed a well-differentiated adenocarcinoma, which was limited to the submucosa (pTNM stage I). The patient has since done well with no signs of recurrence for the twenty-two months that have elapsed since the second operation was performed. Since the incidence of double cancer in the esophagus and stomach is high, and cases such as that described here will be detected more and more frequently in the future, not only a thorough investigation of a stomach intended for use in the reconstruction of the esophagus, but also strict postoperative checkups of the gastric tube when the esophagus has been reconstructed using the stomach must be considered of great importance.