A package includes a magnetic tape cartridge that has a case with an identifier displayed on a front surface, a storage member that has an opening portion, through which the magnetic tape cartridge is put in and out, and in which the magnetic tape cartridge is stored in a state in which the identifier is readable, and a packaging member that covers at least the opening portion of the storage member.

A library device includes: a housing for accommodating a magazine to be able to be put in and out, wherein the magazine has slots for accommodating recording medium cartridges to be able to be put in and out; an accessor for conveying the recording medium cartridge ejected from the slot to the magnetic tape drive; and a cartridge jump-out preventing mechanism for preventing the recording medium cartridge from jumping out to a moving path of the accessor. The cartridge jump-out preventing mechanism includes: an elastic pushing mechanism which can push the recording medium cartridge into the slot by using an elastic force when the magazine is inserted into the housing; and a latch mechanism which can hold the recording medium cartridge so that the recording medium cartridge does not jump out of the slot when the recording medium cartridge is completely accommodated in the slot.