A medium storage device includes a safe having at a front portion a first entrance for replenishment and recovery to which a first transit cassette is selectively connected and at a rear portion a second entrance for replenishment and recovery to which a second transit cassette is selectively connected; an identification unit serving to identify whether the medium is a normal medium or a rejection medium; a recycle cassette configured to accommodate the medium recognized as the normal medium; a conveyance path configured to convey the medium between the first entrance, the second entrance, the identification unit, and the recycle cassette; and a control unit is configured to control the conveyance path such that the medium accommodated in the first transit cassette is conveyed to the identification unit, and the medium identified as the normal medium in the identification unit is conveyed to the recycle cassette.