Patent ID: 6865144

Claim:
An optical pickup apparatus for illuminating a recording surface of a recording medium with a light beam to record and/or reproduce information, comprising: a photodetector for receiving a diffracted light reflected from said recording medium; and a tilt detector for detecting a tilt amount of said recording medium on the basis of a light intensity within an interference region of a 0th-order diffraction light and at least one diffraction light other than the 0th-order diffraction light of the reflected light received by said photodetector wherein said photodetector has three photo-detecting elements arranged in a tangential direction of said recording medium, a radial tilt signal S representing a radial tilt amount being expressed as S=L 1 −L 2 + L 3 provided that reception signals by the photo-detecting elements are given by L 1 , L 2 and L 3 in order with respect to the tangential direction.