in a magnetic tape cassette case including an accommodating portion , a lid portion and a connecting portion for connecting the accommodating portion and the lid portion . the case has movement preventing member capable of accommodating magnetic tape cassettes having different sizes for preventing a small one of the magnetic tape cassette from moving in the case , is provided at least at any one of the accommodating portion , the lid portion and the connecting portion . accordingly , it is possible to provide a magnetic tape cassette case capable of accommodating magnetic tape cassettes having different sizes without play .