PURPOSE: To attain smooth adjustment by inserting a resin-made indentator and a coil spring into a screw hole formed to a pickup base, screwing a screw component and adjusting the pressing force of the coil spring to adjust an angle between a track on a disc and spots thereby supporting the diffractive grating without a play.

CONSTITUTION: The diffractive grating is adjusted by turning the initial position of the 3 spots within a face orthogonal to the optical axis of the diffractive grating 1. A screw hole 2b is provided to the pickup base 2, the resin-made indentator 43 is inserted thereto, its tip is projected to a gap between the diffractive grating holder 1 and the pickup base 2 to press the peripheral face of the diffractive grating holder 1. Further, the coil spring 42 is inserted in the screw hole 2b and the spring pressure of the coil spring 42 is adjusted by adjusting the screw component 41. Thus, the depressing force of the resin-made indentator 43 to the diffractive grating holder 32 is adjusted and the gap between the pickup base 2 and the diffractive grating holder 32 is adjusted.