A process for producing a polymer, characterized in that a polymer having juts is produced by carrying out photopolymerization of at least one photopolymerizable polymerization precursor containing a photocurable compound having two or more unsaturated bonds by irradiation with active energy ray, optionally in the presence of at least one additive component for adding a polymer function, in a supercritical fluid or subcritical fluid; and a polymer having juts of 10 nm or more height, which height is 0.1-fold or more of the diameter of the juts, produced by the above process.