PURPOSE: To reduce the thickness of the optical head by executing the effect of changing the direction of light and the effect of convergence, etc. of light by means of one lens.
CONSTITUTION: Both of the incident surface 18a and exit surface 18b of the lens 18 have a convex face shape and this lens is made into the shape having a flat intra-lens body reflecting surface 18c, the normal of which is the bisector of the intersection angle of the optical axis K1 of the incident surface 18a and the optical axis K2 of the exit surface 18b. The light emitted from a laser light source 15 is refracted by the incident surface 18a and is reflected in a perpendicular direction by the reflecting surface 18c. This light is refracted by the exit surface 18b and is converged to the signal surface of a disk 1. The return light reflected by the disk surface is diffracted by a hologram element 17. The primary diffracted light thereof heads toward a photodetector 16. The detector 16 receives this light as a reproducing signal or focusing/ tracking control signal. The thickness of the objective lens part is reduced in this way and the formation of the optical head to the smaller thickness is possible.