A molding compound in swelling gel phase is prepared by crushing a swelling gel, swelled with a monomer in liquid phase which polymerizes a compound having three-dimensional linking by a radical polymerization reaction, into a predetermined size, and a molding compound (z) is made to adhere to a surface of the molding compound in swelling gel phase so that color difference between a color tone of the molding compound (z) and a color tone of the molding compound in swelling gel phase is not less than 3 in a case where the molding compound (z) is provided on the surface of the molding compound in swelling gel phase, which does not substantially dissolve in the monomer and has a weight change ratio ranging from 0 to +200% in a case where the molding compound in swelling gel phase is completely impregnated with the monomer, so that the molding compound in swelling gel phase and the molding compound (z) are molded under a thermal pressure, and a ratio of the molding compound (z) to a total amount of the molding compound (z) and the molding compound in swelling gel phase is not less than 0.01 weight % and not more than 30 weight %.