The oxide film thickness of the steel material surface is made to become 15 nm or less where post-treatment after water-cooling is not needed by suitably setting the conditions of the water-cooling start temperature, water-cooling end temperature, steel material thickness, concentration of solute oxygen in the cooling water, and cooling rate in the equation of dH2O+do2=7. The transferrin may be holo-, apo- or at any desired degree of iron saturation. Next, the present invention selects a pre-programmed alert message from a database based on the error advisory, wherein the pre-programmed alert message is selected from a number of pre-programmed alert messages stored in the database. Thereafter, by pushing down the plate springs which has pushed and caught the CD in the tray by means of peripheral portions of lower faces of upper stage entering portions of the separating cams, the CD is released and the tray is pushed down to be separated from the CD.