Abstract: A method for manufacturing a compound solid fertilizer is disclosed in which, inexpensive chlorides such as potassium chloride, ammonium chloride and so forth are used as supplementary fertilizer components to be admixed with a phosphate or silicophosphate gel-sol mixture prepared by mixing phosphoric acid with the aforementioned inorganic compound minerals consisting principally of iron, aluminum, magnesium and others. During granulation and hardening, resultant combined chlorine is separated and recovered in the form of hydrochloric acid to minimize the chlorine radical content, thereby permitting not only the manufacture of a fertilizer with practically no bad effect on soil but also the fabrication of hydrochloric acid. Concentrated phosphoric acid, such as super phosphoric acid or concentrated phosphate can be used as the phosphoric acid. A slow-working fertilizer raw material can be further mixed with the gel-sol mixture.