To provide a magnetic tape library device with which a plurality of housed magazines can be extracted safely from the device with the same operation, while the device is made to be simple. The magnetic tape library device includes: a plurality of magazines for housing a plurality of magnetic tape cartridges inside thereof; a device main body for housing the magazines within a same plane in a freely movable manner and in series in an inserting/extracting direction from an inserting/extracting slot; a connecting mechanism for enabling the plurality of magazines to be connected with each other or to be released by a releasing operation from outside; and a locking mechanism for enabling at least the magazine on the back side of the inserting/extracting direction of the device main body, among the plurality of magazines, to be locked or to be released from the locked state at the inserting/extracting slot side.