An optical pickup including a many-sided reflection prism formed as a single body with a plurality of reflection faces to guide a light beam incident through a transmission face in a horizontal direction perpendicular to a height direction by reducing a size of the light beam in the height direction, by using a difference in angles between the reflection faces, and to reflect the guided light beam in the height direction by one reflection face of an angle less than 45° with respect to the horizontal direction. By using the many-sided reflection prism, the height of an optical system can be reduced regardless of the wavelength used without reducing light beam size. Thereby, slim-sized optical pickups can be implemented.