Abstract: A laser emission unit for use in an optical head performs a plurality of functions which are integrated. A laser beam from the laser emission unit mounted in a lens holder is emitted through an objective lens and is focused on an optical medium. A reflected beam from the optical medium returns through the objective lens and a diffraction grating to a signal detection circuit in the laser emission unit. Since the laser emission unit performs a plurality of functions, the space for various elements otherwise required in the optical head can be eliminated. The space for an additional light path for the reflected beam is also eliminated. Therefore, the size of the optical head is very small. Since the optical head can be assembled by using a small number of parts, the production costs can be reduced. Furthermore, the optical head can shield the noises by using the housing and/or the lens holder itself.