PURPOSE: To enable adjustment of a positional relation with high accuracy regardness of mechanical accuracy of respective parts by using mirrors so that the exit light to an optical disk is made coincident with the light reflected from the optical disk.

CONSTITUTION: The method for adjusting an optical disk in the stage of assembling the same is executed by lighting first a light source 24, reflecting the ray from the light source 24 by the mirror 25 and irradiating the ray through a half mirror 23 to the optical disk 3. The return light from the disk 3 traces backward the same optical path and is detected by a photosensor 26 for sensing the return light if the disk 3 intersects orthogonally with the optical axis of the mirror 23, i.e., if the disk 3 is exactly parallel with the top surface 21A of a head housing 21. Said light is not sensed by the photosensor 26 when the disk 3 is not parallel with the surface 21A of the head housing and therefore the attaching attitude of the disk 3 is corrected until the disk 3 is made parallel with the top surface 21A of the head housing.