At least one of a hollow particle 14, a porous particle 24, and a solid particle 34 having the pores 18, 28, 38 on the surface thereof is subjected to plasma irradiation under a reduced pressure while changing plasma irradiation intensity and/or the degree of vacuum. After the plasma irradiation, at least one type of monomer is graft polymerized onto the surface of the plasma irradiated particle by contact between the at least one type of monomer and the particle so as to substantially fill the pores 18, 28, and 38 of the particle with grafted polymers 12 of the monomers.