A method of adjusting spherical aberration correction and focus offset of a light beam. A first approximate straight line is detected indicating a first relationship between the spherical aberration correction and the focus offset according to a first evaluation index indicating a quality of cross-track signal. A second approximate straight line is detected indicating a second relationship between the spherical aberration correction and the focus offset according to a second evaluation index indicating a quality of a reproduced signal. A spherical aberration correction value and a focus offset value, to be adjusted, are determined from an intersection of the first approximate straight line and the second approximate straight line.