Porous and easy water soluble amorphous silicon, method and apparatus to produce thereof can be obtained which does not contain tar, crystal, residual agrichemicals, and carcinogens by using only one burning treatment from a plant including silicon abundantly such as rice plant like as rice husks constituting rice, rice straw, rice bran, wheat, corn, grass and horsetails, tea, potato and the like. It is a method of manufacturing an amorphous silicon which is porous and easily soluble in water and which does not contain tar, crystal, residual agrichemicals and carcinogens, which comprising, burning the rice husks, etc. at the temperature range of between 500° C. or more and 700° C. or less, while stirring the rice husks, etc., by introducing at atmospheric gas having a mass of 6.7 times or more and 20 times or less of the weight of the rice husks, etc., oxygen gas having a weight of 1.4 times or more and 4 times or less with respect to the weight of the rice husks, etc., or mixed gas of the atmospheric gas and the oxygen gas into the furnace, at the same time as burning, combustion gas generated at the time of combustion rice husks, etc. is discharged from the furnace.
