PURPOSE: To improve the productivity of a servo disk by using an optical servo disk so as to record servo information for positioning of a magnetic head by means of a pit changing the light reflectance.

CONSTITUTION: One or plural magnetic disks 1 are overlapped together, they are fixed to a rotary shaft to record/reproduce information. A magnetic head 2 is provided to both sides of the disks 1 and an information recording and reproducing device 3 uses the head 2 to control a signal recording or reproduc ing the information. An optical servo disk 4 uses a pit reflecting light so as to record the positioning servo information positioning the head 2 to the disk 1 recording and reproduction a signal and the servo information recorded on the disk 4 is detected optically by the servo information optical detection head. A magnetic head positioning device 6 receives a servo information signal outputted from a head 5 to apply positioning control to the head 2 at an object position. Thus, the productivity of the servo disk is improved.