PURPOSE: To improve an information reproducing capability by providing with a prism having a polarized surface in which a laser beam from a laser beam source is transmitted and a polarized beam is reflected, a 1/4 wavelength plate on an optical axis and a light receiving element receiving a reflected beam.

CONSTITUTION: A reading assembly 28 is provided with the prism 30 having the polarized surface in which the laser beam 26 from the laser beam source is transmitted and the polarized beam 38 is reflected, a 1/4 wavelength plate 36 arranged on the optical axis between the polarized prism 30 and an objective lens 52, and the light receiving element 40 receiving the reflected beam reflected with the polarized surface 30 of the prism. Therefore, although the reflected beam passes through a polarized beam splitter prism 30 twice at the time of incidence and reflection, the reflected beam finally reaching the light receiving element 40 is hardly damped. By this way, the sufficient information reproducing capability is obtained without necessitating a laser element having a specially high beam intensity and a light receiving element having a specially high light receiving sensitivity.