PURPOSE: To allow the release of the gases and microparticles which exist in the optical disk and generates at the time of recording to the outside.

CONSTITUTION: Holes 11a to 11e, 12a to 12e as air flow passages are provided between an outer spacer 3 and inner spacer 4 installed to form an air layer 5 between disk substrates 1a and 1b of the optical disk medium of an air sandwich type. The gases and microparticles generated at the time of recording to recording layers 2a, 2b are released to the outside through these holes 11a to 11e, 12a to 12e.