A method for finely feeding granular solids into a liquid, in which method granular solids and a liquid are fed into a mixing space and mixed together, and a mixture of small solid particles and liquid is discharged from the mixing space. The granular solid matter in the mixing space is subjected to a liquid flow in such a manner the granular solids are brought to roll controllably in a controlled rolling space locating in the mixing space, whereby the grains of the granular solids abrase one another while rolling and tiny particles detaching in abrasion are carried away from the mixing space along with the liquid and large grain particles continue rolling in the controlled rolling space.