A method and optical disc apparatus for evaluating a quality of a read signal adapted to the PRML method by evaluating a binary code decoded from the read signal obtained by a head, in which an error bit sequence having one bit edge shift from the binary code is generated, a Euclidian distance is calculated on both a correct bit sequence and the error bit sequence with respect to a predetermined target signal level, assuming that the binary code is the correct bit sequence, a Euclidian distance difference between the Euclidian distance on the correct bit sequence and the Euclidian distance on the error bit sequence is calculated, an average Euclidian distance from the target signal level is calculated, a normalized sequence error is calculated, the binary code is evaluated using the normalized sequence error.