A modified silicone compound having a branch polymer comprising a hydrophilic group, this compound being synthesized by performing an addition reaction between an organohydrogenpolysiloxane, and at least one compound chosen from an alkenylated polyoxyalkenylated compound, an alkenylated glycerine compound and an alkenylated sugar in the presence of a platinum catalyst or rhodium catalyst, and a cosmetic material containing this modified silicone compound. This compound is purified by decomposing aldehyde condensation products remaining in the silicone by alkylating the remaining unsaturated bonds after hydrogenating the reaction liquor after said addition reaction, and treating with an aqueous solution of pH 7 or lower containing an acidic substance, or decomposing the propenyl etherated polyether in the reaction liquor after said addition reaction by treating with an aqueous solution of pH 7 or lower containing an acidic substance, and then alkylating the generated aldehydes and alkenylated ether compounds by hydrogenation. The degree of unsaturation (meq/g) in the modified silicone compound is 0.002 or less. The generation amount of aldehydes when heat ageing is performed in 0.23N hydrochloric acid at 50° C. for 0.5 hours is 70 ppm or less of the modified silicone compound.