A tape cassette has a substantially rectangular, box-shaped casing with a recess in a front portion of the casing having openings facing forwardly and downwardly, respectively, and with a bottom wall of the casing having an undersurface including cassette height determining portions adjacent the front and back of the casing and a slide surface portion therebetween which is planar and recessed relative to at least the cassette height determining portions adjacent the back of the casing. A lid is pivotally mounted on the casing for movements between a closed position extending across the opening facing forwardly from the recess and a raised opened position uncovering the forwardly facing opening, and a tape is wound about reels rotatable in the casing and extends between the reels in a path including a run extending across the forwardly facing opening so as to be disposed in back of the lid in its closed position. A shutter includes a lateral portion extending across the undersurface of the bottom wall and being slidable relative to the slide surface portion between a closed position in which the shutter closes the opening facing downwardly from the recess and a rearwardly displaced opened position uncovering such opening. The lateral portion of the shutter is dimensioned to be contained within the recessed slide surface portion in at least the opened position of the shutter so as to avoid any interference with access to the cassette height determining portions of the undersurface.