PURPOSE: To prepare a soya milk product free from the characteristic unagreeable odor of bean juice easily, by immersing dried soybeans in hot water for a short time, heating the swollen soybeans with hot steam to inactivate the sporal enzyme and boil the swollen soybeans, and grinding the boiled soybeans.

CONSTITUTION: The shower head 20 to eject hot water is attached to the top of the hopper 12 for supplying soybeans, and the cylindrical jacket 17 to blast steam into the hopper 12 is attached around the lower circumference of the hopper 12. The soybean grinding chamber 1 is positioned below the jacket 17 interposing a hot-water ejection chamber 23, and the chamber 1 is furnished with the stationary grindstone (a) and the rotary grindstone (b), and with a ring- shaped steam jacket 11 at the circumference of the chamber 1. The stirring blade 22 and the metering screw 24 are placed in the hopper 12. The dried soybeans are immersed in hot water for a short time, the swollen soybeans are heated with hot steam to inactivate the sporal enzyme and at the same time to boil the beans with hot steam, and the heat-treated soybeans are ground in a chamber 1 having hot atmosphere. Accordingly, a soya milk product free from the characteristic odor of bean juice can be prepared easily.