The present invention relates to an optical disk reproducing apparatus, and provides a technology capable of supporting even a situation in which a reproduction signal characteristic is changed due to a factor other than recording density of an optical disk by using PRML of different constrained length and capable of improving reading accuracy. The optical disk reproducing apparatus includes a PRML circuit of first constrained length (for example, 4) and a PRML circuit of second constrained length (for example, 5). Equalization error values obtained during calculation of equalization learning in respective circuits are compared with each other in a determination circuit. Switching control of a switch is performed so that an output of one of the PRML circuits having a smaller equalization error value is selected.