An automatic cassette changer capable of selectively loading any of cassettes (1, 2) of various sizes upon a recording and/or playback unit (13), comprises cassette-housing racks (3) capable of selec­tively storing any of large cassettes (1) and small cassettes (2), and having first guides for the large cassette and second guides for the small cassette so as to put the respective cassettes in their proper positions; and a cassette transfer (10) having third guides for the large cassette (2) and fourth guides for the small cassette (1) so as to have both sides of the respective cassettes guides, and capable of selectively moving any of the large cassette and the small cassette from the cassette-housing racks (3) to the recording and/or playback unit (13), and vice versa.