A tape cassette (1) has a substantially rectangular, box-shaped casing (2) with a recess (7) in a front portion of the casing (2) having openings facing forwardly and downwardly, respectively, and with a bottom wall (4A) of the casing (2) having an undersurface (4a) including cassette height determining portions (41a, 41b) adjacent the front and back of the casing (2) and a slide surface portion (40) therebetween which is planar and recessed relative to at least the cassette height determining portions (41a, 41b) adjacent the back of the casing (2). A lid is pivotally mounted on the casing (2) for movements between a closed position extending across the opening facing forwardly from the recess (7) and a raised opened position uncovering the forwardly facing opening, and a tape (5) is wound about reels (6) rotatable in the casing (2) and extends between the reels (6) 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 (20) includes a lateral portion extending across the undersurface (4a) of the bottom wall (4A) and being slidable relative to the slide surface portion (40) between a closed position in which the shutter (20) closes the opening facing downwardly from the recess (7) and a rearwardly displaced opened position uncovering such opening. The lateral portion (21) of the shutter (20) is dimensioned to be contained within the recessed slide surface portion (40) in at least the opened position of the shutter (20) so as to avoid any interference with access to the cassette height determining portions (41a, 41b) of the undersurface.