An information recording and reproducing apparatus that is smaller in size, high in disk exchange speed, loaded with optical disks and large in capacity is provided by providing an information recording and reproducing apparatus comprising a cartridge loaded with optical disks, a head for recording information on and reproducing information from one of the optical disks, a spindle for rotating the optical disk, and a first robot arm for carrying the optical disk between the cartridge and the spindle, the first robot arm being variable in length, the cartridge being expandable and contractible in a direcition perpendicular to the surface of the optical disk.