There are disclosed recording/reproducing devices for use with computers and particularly for recording or reproducing desired information on or from recording mediums like floppy disks, the devices being miniaturized and reduced in thickness for adapting themselves to the miniaturized computers of nowadays. The reduction in device thickness involves the use of a small-sized rare earth group magnet and neodymium ferrous boron which have good magnetic properties as rotor magnets of disk and carriage driving motors; or alternatively planar superpositions are avoided when placing the disk driving motor and the carriage or a carriage guide shaft and a circuit board. The thinned recording/reproducing devices contribute to diminishment of a space for accommodating the computer to meet a demand for miniaturization thereof. A plurality of miniaturized recording/reproducing devices of the invention can be set in the existing space for placement.