An optical pickup apparatus comprises an objective lens for converging a light beam onto an optical recording medium, and a light guide disposed so that the surface thereof receives the light beam reflected by the optical recording medium. A focusing grating is provided on one surface of the light guide for introducing the reflected light beam into the light guide such that the reflected light beam advances by total reflection between the one surface and the other surface of the light guide, and converging the light beam thus guided in the light guide. A photodetector secured to the surface or an edge face of the light guide detects the guided light beam converged by the focusing grating. Tracking error, focusing error and signals recorded on the optical recording medium are detected based on an output of the photodetector.