An optical-pickup apparatus includes: a three-wavelength-laser diode including first-, second-, and third-laser elements to emit first-, second-, and third laser beams having first, second, and third wavelengths, respectively, the three laser elements housed in the same case; an objective lens to focus the three laser beams onto first- to third-optical-disc-signal-recording layers, respectively; a first photodetector to be irradiated with first-return light reflected from the first-optical-disc-signal-recording layer, a second photodetector to be irradiated with second- and third-return lights respectively reflected from the second- and third-optical-disc-signal-recording layers; a polarizing-beam splitter to reflect the three laser beams toward the lens, and allow the three return lights having passed through the lens to pass therethrough; a semitransparent mirror on which the three return lights having passed through the polarizing-beam splitter are incident, and which guide the first-return light toward the first photodetector and the second- and third-return lights toward the second photodetector.