A molding machine for production of gas hydrate pellets under a high pressure in gas hydrate forming conditions, which is inexpensive through minimizing of the use of expensive mechanical seal. The molding machine comprises two forming rolls each fitted to a rotary shaft whose both ends are supported by bearings; a drive unit for rotating the forming rolls; a screw transfer unit for supplying powder to the forming rolls; and a high-pressure vessel, wherein the bearings, the rotary shaft and the forming rolls are all disposed in the high-pressure vessel.