In an apparatus and a method for processing digital signals in an optical disc system, the digital signal processing apparatus includes an EDC unit that processes data that is demodulated by an EFM demodulator to determine in advance whether input data requires error correction. When EDC determination indicates that the input data has no errors, the apparatus does not carry out error correction on the data. Only when it is determined that the input data has errors, the apparatus performs error correction. Accordingly, data processing efficiency is improved. The digital signal processing apparatus repeats error correction on data having errors to a maximum of n times according to the quantity of errors. The number of error correction repetitions is made variable in order to maximize error correction capability. Furthermore, the apparatus converts erasure information generated when EFM demodulation is carried out into erasure location on a GF(2^8) field and adds a 10-byte erasure location to the back of the parity of each PI codeword to use it for PI erasure correction. Accordingly, PI erasure correction can be efficiently performed.