PURPOSE: To improve the availability of a second harmonic beam for reading a recording signal by using a basic beam outgoing from an SHG laser for detecting an error signal.

CONSTITUTION: This device is constituted of an SHG laser light source 1 emitting the basic beam and the second harmonic beam, an optical system 2 enlarging a laser beam outgoing from the laser light source, the optical systems 4, 5 changing a polarization condition, the optical system 6 converging to a minute spot on the recording surface of an information recording medium 7, the optical system 3 leading a reflected luminous flux from the recording medium to a photodetector and a second harmonic separator 8 separating the laser beam. The solid laser beam of the reflected luminous flux from the optical system 3 is reflected by the separator 8, and the astigmatism is formed by a cylindrical lens 9, and the laser beam is made incident on the photodetector 11 for error signal by a condenser lens 10, and the error signal is detected by an astigmatic method and a push-pull method. On the other hand, the second harmonic beam transmits through the separator 8, and is made incident on the photodetector 13 for information signal by the condenser lens 12 to detect the recording signal.