PURPOSE: To miniaturize a size and to reduce a weight by substituting a lens and other optical parts for holographic optical elements and constituting one module of an optical detector and laser diode.

CONSTITUTION: A laser beam reflected by optical disk 40 is focused by a first and second holograms H1 and H2. This focused beam is detected with optical detectors 60a and 60b for tracking detection, and because of an increase in quantity of light in a part 'a', a signal detected with an optical detector 60a becomes larger than the one detected with an optical detector 60b. In this case, since it is possible to constitute one module of a laser diode and an optical detector, not only a reading speed is accelerated but also inexpensive mass- production becomes possible and the optical pickup device can be reduced in size and weight.