A swing-arm type optical recording and reproducing apparatus and an optical disk applicable to the same. The optical disk includes a substrate having an information recording surface to record and reproduce an information signal, and a protective layer which is provided on the information recording surface and whose surface facing a slider is a flat even surface so that variations in a floating height of the slider can be reduced. The optical recording and reproducing apparatus further includes, an optical head having a light source provided at a swing arm to emit light of a predetermined wavelength; an optical path changing means provided in the optical path of the light emitted from the light source for changing the proceeding path of incident light; a collimating lens installed at the slider to preliminarily converge the light emitted from the light source and entering via the optical path changing means; an objective lens installed at the slider to converge the light which is emitted from the light source and enters via the optical path changing means to form an optical spot on the optical disk; and a photodetector to receive the light which is reflected from the optical disk and enters via the objective lens, the collimating lens, and the optical path changing means. The optical head detects an information signal and an error signal in order to reduce defocus due to variations in ambient temperature and variations in the wavelength of the light of the light source.