An optical pickup for recording on and reproduction from recording media of different recording densities (e.g. a high density disk such as a DVD and a lower density disk such as an ordinary CD), and having a compact, thin and low power-consumption design. The optical pickup includes an objective lens, a first optical unit having a light-emitting element and a light-receiving element which are used for recording on and reproduction from the high-density optical disk, a second optical unit having a light-emitting element and a light-receiving element which are used for recording on and reproduction from the low-density optical disk, a beam splitter for guiding optical axes of the first and second optical units to the same optical axis, and a wavelength filter for changing a diameter of light beams incident on the objective lens between at the time of recording and reproduction for the high-density optical disk and at the time of recording and reproduction for the low-density optical disk.