PURPOSE: To manufacture the product of uniform particle size being uniformly coated with the oxide film at a high productivity, by stirring and heating the kneaded material consisting of granular silicon as the base material and the peroxide solution, and after that, by further heating to higher temperatures.

CONSTITUTION: The granular metallic silicon or silicon alloy and the peroxide solution at a specified proportion are charged into the mixer and are thoroughly kneaded; hereby, the peroxide solution is uniformly applied to the surface of the granular silicon. This granular material is discharged from the mixer, and is stored in the hopper, and then, is supplied from this hopper to the external combustion type rotary drier continuously. Within the rotary drier, the granular material is heated to about 400°C while being stirred, and is mutually unbound from other pieces; as a result, the deposit of peroxide is formed on the surface of granular material. This granular material is continuously discharged from the drier and is stored in the hopper; from this hopper, the granular material is continuously charged into the rotary kiln. The granular material is heated to about 800°C in the rotary kiln, and is taken out as the product, being followed by the cooling.