To excellently detect and correct spherical aberrations even in a state, in which a peak of total signals from divided light-receiving elements which receive returned light from an optical recording medium does not accord with a position at which defocus becomes "0" in variations (S curve) of focus error signals, without complicated composition, jumbo-sized composition and an increase in production cost.

Returned light from a signal recording surface of an optical recording medium 1 is received by a quadripartite light receiving element 10 via an astigmatism-generating element 9. A spherical aberration is detected based on which is larger in distortion, a sum signal of light detection signals from one light-receiving area or that from the other light-receiving area, these two light-receiving areas belonging to the four light-receiving areas obtained by dividing the quadripartite element 10 into four areas and being diagonally located to each other. The correction of the spherical aberration is carried out based on the detected spherical aberration.

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