An optical pickup records data in or reproduces data from optical recording media respectively having recording faces at different heights, and includes a semiconductor laser diode array having light emitting portions for respectively emitting laser beams of different wavelengths. A finite conjugate type object lens used in this optical pickup is designed so that the numerical aperture of the object lens can be controlled to be changed in accordance with switching between the different wavelengths for allowing a laser beam to be focused on each optical recording medium.