A 37-year-old male was admitted to our hospital because of an abdominal tumor, about the size of a fist, located anterior to the pancreas head. This tumor oppressed the antrum of the stomach to the left, and an operation was performed, the tumor being diagnosed as a leiomyosarcoma of the stomach, determined from image findings. After histopathological examination, however the tumor proved to be an adenocarcinoma. An early gastric cancer was found at the anterior wall of the antrum during the operation, and the tumor was thought to be a metastatic lymph node. Lymph node metastasis also was observed at the root of the mesentery.