PURPOSE: To inhibit fine foreign matter and protrusions from biting into the contact surfaces of an optical disk and a magnetic head and to prevent the damage of the surface of the optical disk by reducing the frictional resistance of the contact surfaces by lubrication.

CONSTITUTION: A sliding material 11 is stuck to the inside of the side B of an optical disk case 9 except a part corresponding to the window of a shutter 10. When an optical disk 1 is not used, it comes in contact with the sliding material 11 and the lubricating component of the sliding material 11 sticks to the surface of the disk 1 coming in contact with a magnetic head 7. The frictional resistance of the contact surfaces of the disk 1 and the head 7 is reduced and the head 7 is floated by the lubricating component. As a result, even if foreign matter and protrusions collide against the head 7, the shock is relieved.