Patent ID: 7839743

Claim:
An optical disc apparatus comprising: a plurality of light sources emitting light beams having different wavelengths respectively; a plurality of objective lenses one of which is disposed selectively in a light path in response to an optical recording medium to condense on a recording surface of the optical recording medium a light beam emitted from one of the plurality of light sources, which is selected in accordance to the optical recording medium; a spherical aberration compensating element disposed between the plurality of light sources and the objective lens disposed in the light path to perform compensation of spherical aberration; a memory portion memorizing information; an amplitude obtaining portion obtaining S shaped waveform of focus error signal by emitting the light beam from one of the plurality of light sources and moving the objective lens disposed in the light path in an optical axis direction and obtaining amplitude from the S shaped waveform; and a discriminating portion changing controlled variable of the spherical aberration compensating element into a plurality of prescribed control values, obtaining, for each of the plurality of prescribed control values, the amplitude of S shaped waveform from the amplitude obtaining portion, and performing discrimination to determine whether one of the plurality of objective lenses is disposed in the light path based on the differences of changing rates of the amplitude of S shaped waveform changed from the controlled variable among the plurality of objective lenses.