We developed equipment to allow continuous treatment of collagen slurry under hydrothermal condition. Using this equipment, we were able to increase the amount of gelatin obtained from calf skin using only water in a reaction time of under 2 seconds at 260 degrees C. The molecular weight distribution of the gelatin can be varied by adjusting the reaction temperature and adding a small amount of a catalyst such as acetic acid. This adjustability is advantageous in the utilization of the gelatin. The gelatin is easily purified, allowing hydrolysis of the collagen in water alone. Therefore this processing technology greatly simplifies the manufacture of gelatin compared with the conventional method.