A tape cassette that includes a box-shaped cassette case whose outline being defined by a bottom wall, a top wall, and a side wall and including a plurality of corner portions, at least one tape contained within a tape containment area defined within the outline, a pair of cavities extending from the bottom wall and being provided between the tape containment area and the outline at opposite ends of a diagonal line connecting one of the corner portions to another of the corner portions, and a side face indicator portion provided in the side wall, indicating a type of the tape, and including a plurality of indicator portions disposed in a pattern in accordance with the type of the tape, each of the indicator portions being one of a switch hole and a surface portion.