We encountered a case of gastric cancer that was initially detected as a deep hemorrhagic ulcer without surrounding irregular elevation, followed by rapid protrusion in less than 1 month. Using endoscopic images in the follow-up study, we estimated the doubling time (DT) of this unusual tumor as 9.2 days. Since the doubling time of gastric cancer is generally fairly long due to exfoliation of many cancer cells into the gastric lumen, this cancer presented with extremely rapid growth. Besides, this case reinforces that follow-up study is important in terms of clinical management of ulcerative lesions.