Provided is a particle suitable for a specimen test, which has high sensitization efficiency in a reaction with an antibody, shows high detection sensitivity as a latex reagent, hardly agglutinates during its storage, and hardly causes nonspecific adsorption even when not post-coated. The particle is a particle including a copolymer containing a monomer unit derived from a styrene-based monomer and a monomer unit derived from a glycidyl group-containing monomer, the particle being represented by the following general formula (1): in the general formula (1), L1 represents a copolymer moiety containing the monomer unit derived from the styrene-based monomer and the monomer unit derived from the glycidyl group-containing monomer, “n” represents from 4 to 11, and R1 and R2 each represent a hydrogen atom, an alkyl group, or a halogen.