PURPOSE: To output an output signal at an appropriate output level from an information read device by adjusting the intensity of light emitted from a light source in an optical path by an output adjusting device based on an information reproducing signal outputted from the information read device.

CONSTITUTION: Laser light emitted from a semiconductor laser 2 passes a polarizer 12 and forms a light spot on the information recording surface 1a of an optical disk 1 through a diffraction grating 13, a beam split prism 4 and an objective lens 5. Then, an output adjusting device 16 adjusts the intensity of the laser light emitted from the simiconductor laser 2 in the optical path based on the result of comparison 13 between the voltage of the information reproducing signal outputted from a photodetector 7 and a reference voltage 14. While the S/N of the laser light is set in the best condition at the stage that the laser 2 emits the laser light, the intensity of the laser at the stage that the laser light is inputted in the photodetector 7 is adjusted without deteriorating the S/N of the laser light after it is emitted, and the photodetector 7 generates and outputs the information reproducing signal at the appropriate level, a focus error signal and a tracking error signal.