A tape cassette comprising: a generally rectangular box-like housing having a top wall, a bottom wall, and a side wall defining a periphery of the housing, the top wall and the bottom wall form rectangular planar portions oppositely arranged in a vertical direction; a first cavity provided in the bottom wall and disposed in a first corner portion of the bottom wall; a tape feed roller rotatably supported inside the first cavity; a second cavity being a groove formed in the side wall, disposed in a second corner portion, the second corner portion being located at a diagonal position with respect to the first corner portion of the bottom wall, the side wall in which the groove is formed forming a right side surface or a rear side surface of the tape cassette; the first and second cavities (64, 47) extending from the bottom wall and disposed between a tape containing area and the periphery at opposite ends of a diagonal of the generally rectangular box-like housing, the tape containing area being defined within the periphery, and the diagonal connecting the first corner portion and the second corner portion of the generally rectangular box-like housing; at least one tape (55, 57, 58, 59) wound and mounted within the housing in the tape containing area defined within the periphery, the at least one tape including a first tape (55, 57, 58) disposed in a first area, the first tape having a hole at a center of winding, the first tape (55, 57, 58) being an unused tape, and the first area being one of two areas (30C and 30D) formed by dividing the housing with respect to a line connecting the first cavity and the second cavity; and a third cavity that extends in the hole of the first tape from the bottom wall, wherein the first and second cavities (64, 47) are for guiding the tape cassette when the tape cassette is installed in or removed from the tape printer,wherein, when the side wall forms the right side surface of the tape cassette, the groove is concaved toward a left direction in a plan view over the entire height of the housing or along the line in a plan view, wherein, when the side wall forms the rear side surface of the tape cassette, the groove is concaved toward a front direction in a plan view or along a direction perpendicular to the line in a plan view, and wherein the tape feed roller is configured to pull out the first tape (55, 57, 58) in concert with a corresponding movable feed roller of the tape printer when the tape cassette is installed in the tape printer. a generally rectangular box-like housing having a top wall, a bottom wall, and a side wall defining a periphery of the housing, the top wall and the bottom wall form rectangular planar portions oppositely arranged in a vertical direction; a first cavity provided in the bottom wall and disposed in a first corner portion of the bottom wall; a tape feed roller rotatably supported inside the first cavity; a second cavity being a groove formed in the side wall, disposed in a second corner portion, the second corner portion being located at a diagonal position with respect to the first corner portion of the bottom wall, the side wall in which the groove is formed forming a right side surface or a rear side surface of the tape cassette; the first and second cavities (64, 47) extending from the bottom wall and disposed between a tape containing area and the periphery at opposite ends of a diagonal of the generally rectangular box-like housing, the tape containing area being defined within the periphery, and the diagonal connecting the first corner portion and the second corner portion of the generally rectangular box-like housing; at least one tape (55, 57, 58, 59) wound and mounted within the housing in the tape containing area defined within the periphery, the at least one tape including a first tape (55, 57, 58) disposed in a first area, the first tape having a hole at a center of winding, the first tape (55, 57, 58) being an unused tape, and the first area being one of two areas (30C and 30D) formed by dividing the housing with respect to a line connecting the first cavity and the second cavity; and a third cavity that extends in the hole of the first tape from the bottom wall, wherein the first and second cavities (64, 47) are for guiding the tape cassette when the tape cassette is installed in or removed from the tape printer,wherein, when the side wall forms the right side surface of the tape cassette, the groove is concaved toward a left direction in a plan view over the entire height of the housing or along the line in a plan view, wherein, when the side wall forms the rear side surface of the tape cassette, the groove is concaved toward a front direction in a plan view or along a direction perpendicular to the line in a plan view, and wherein the tape feed roller is configured to pull out the first tape (55, 57, 58) in concert with a corresponding movable feed roller of the tape printer when the tape cassette is installed in the tape printer.