Abstract: Rice grains are soaked in water to give a rice-grain soaked liquid to allow the rice grains to absorb water and the entire rice-grain soaked liquid is then charged into a mill to mill the rice grains to prepare finely-divided rice grains containing water absorbed therein and the finely-divided rice grains form a rice paste containing free water present therebetween; the finely-divided rice grains in the rice paste can be fine; and, in addition, since free water is involved upon milling, deterioration of components by heat can be avoided. In addition, the finely-divided rice grains can remain in a water-absorbed state, and damage of finely-divided rice grains (starch simple grains) by drying can be avoided. In addition, since free water increases affinity between a kneaded product of a different kind of cereal flour or other ingredients and the rice paste, mixing thereof can be rapidly carried out.