Optical head, optical disc device, computer, optical disc player and optical disc recorder

An optical head comprising:

• a light source for emitting laser light of 430 nm wavelength or less;
• a collimator lens for converting the laser light emitted from the light source into substantially parallel light;
• an objective lens for collecting the laser light emitted from the collimator lens on an information recording medium having plural information recording surfaces;
• a detecting lens for imparting astigmatism to the laser light reflected on the information recording medium and collected by the collimator lens;
• and
• a light receiving element for receiving the laser light subjected to the astigmatism by the detecting lens, wherein
• the detecting lens is made of a resin material, and
• the detecting lens is disposed on the side of the objective lens with respect to a light collecting position, by the collimator lens, of the laser light reflected on a second information recording surface different from a first information recording surface having a thinnest protection substrate, among the plural information recording surfaces of the information recording medium, in recording or reproducing on or from the information recording surface having the thinnest protection substrate.