The relation between the cover layer thickness of a data recording surface and ratio α of SCO to SCD is previously calculated and stored in a storage unit, where SCD denotes coma aberration which occurs when the data recording medium is tilted by unit angle and SCO denotes coma aberration which occurs when the objective lens is tilted by unit angle. When α1 denotes ratio α for a data recording surface corresponding to the smallest cover layer thickness, tilting angle θ1 of the objective lens is determined based on the α1 and a tilt adjustment of the objective lens is made. Also, when α2 denotes ratio α for a target data recording surface, tilting angle θ2 of the objective lens is estimated based on the ratio of α2 to α1 and a tilt correction of the objective lens is made.