An apparatus and a method of detecting an error symbol in a data storage apparatus so that an error correcting performance of an error correction decoder. The error symbol detecting apparatus includes an equalizer equalizing a signal transmitted to a channel using a channel equalization characteristic that is suitable for a corresponding system, a data detector to detect data from the signal output from the equalizer, a modeling tool designed to have the same characteristics corresponding to a partial response (PR) target polynomial applied to the system, a correlation evaluation information generating unit to generate correlation evaluation information based on a correlation degree between an actual output of the equalizer and a target output of the modeling tool, and an error symbol determination unit to determine an order of probability of error generation of the symbols based on the correlation evaluation information, and to determine a predetermined number of symbols having a high probability of generating errors corresponding to the order of probability of error generation as error generating symbols.