A media cartridge autoloader is disclosed that includes a rotation transmission path forming device. The rotation transmission path forming device includes a drive shaft unit, a drive shaft unit shifting mechanism, and a magazine drive motor module. A mechanism that rotates a turntable of a media cartridge picker is also used to move and selectively couple the drive shaft unit with either one of media cartridge transport magazines positioned near the cartridge picker. A drive shaft of the drive shaft unit is driven by a magazine drive motor of the magazine drive motor module, so that the coupled magazine is driven. A swing pinion meshes with a rack section such that the lock of a door for a mail slot is released with a driving force generated by the magazine drive motor.