To rationally and efficiently control the water content and to improve the productivity of a forming machine and the stability of the quality of a formed article by measuring the hardness of a rod-shaped argil extruded and transported from a kneader, not transporting a nonstandard argil to the forming machine and automatically injecting water into the kneader.

A rod-shaped argil 1 extruded from a kneader is automatically cut to a set length and transported by a belt conveyor 20. Before that, the rear end is detected by a sensor 25, and the conveyor 20 is stopped below a hardness measuring member 30 under the command of a controller. A needle 32 is thrust into the argil 1 by the same command, the thrust amt. is measured by a measuring part 33, and the needle 32 is raised. When the measured hardness of the argil 1 is within a specified range, the conveyor 20 is started to transport the argil 1 to a forming machine. When the hardness is beyond the specified range, the conveyor 20 is inclined by a lift 50, and the argil 1 is rolled to a receiver 51 and sorted. When the hardness of argil exceeds the upper limit, water is added on the instructions to the kneader to the extent of the difference from the specified value.