A magnetic tape cassette in which a cassette housing has half cases with aligned, confronting projections on innder surfaces thereof on which a cylindrical guide roll with an axial bore therethrough is supported, has an annular, axially projecting rib on either the guide rolls or the projections so as to prevent any burrs which may be on the guide roll around the axial bore therethrough from coming into contact with the projections, thereby preventing noise which might otherwise be caused by the burrs.