PURPOSE: To obtain a double refraction prism in which a sufficient component light separation angle is realized using a single prism and to reduce the cost and the size of an optical pickup device.

CONSTITUTION: The optical axis of an optical medium, which constitutes a double refraction prism with an apex angle θ, is placed within an optical axis surface 14 which is set parallel to a ridge line 13 defined by the intersection of a first surface 11 and a second surface 12 in the prism 10. When the signal light reflected from a magneto-optical disk is made incident on the surface 11 with an incident angle α so that the optical axis after refraction is approximately made perpendicular to the surface 14 along the plane (this paper) which is perpendicular to the line 13, two component light beams p and s are emitted from the surface 12. Since the difference between respective deflection angles δp and δs, i.e., a separation angle Δδ, becomes maximum, a sufficient separation angle Δδ is obtained in spite of the fact that the prism 10 is a single prism. Thus, the optical pickup device employing the prism 10 becomes low in price and small in size.