PURPOSE: To open and close a couple of opening/closing covers smoothly by guiding a couple of arcuate parts by a couple of arcuate guide parts when the couple of opening/closing covers are opened and closed.

CONSTITUTION: The couple of opening/closing covers 20 and 21 are pushed and open upward and downward with the front end part 11a of a disk cartridge 1, the insertion pressure of the cartridge 11 is applied as deforming force which flexes the couple of opening/closing covers 20 and 21 toward rear surfaces 20a and 20b in right and left lengthwise directions. The couple of arcuate parts 28 and 29, on the other hand, abut on the couple of arcuate guides 31 and 32 to receive the deforming force, and the couple of opening/closing covers 20 and 21 are prevented from flexing toward the rear surfaces 20a and 20b as shown by imaginary lines. Consequently, the couple of opening/closing covers 20 and 21 are opened and closed very smoothly.