Disclosed is a tape cassette in which two positioning holes is formed in the back surface of a cassette shell. One of the two positioning holes is formed into a circular shape and the other is formed into a long-hole shape. The positioning hole formed into the long-hole shape is divided into two parts in the major direction of the long-hole. An about half of the long-hole shape is used as a positioning hole and an about remaining half thereof is used as an information detecting (ID) hole for providing various kinds of information. A removable block piece is provided on an opening portion of said ID hole. With this configuration, the ID hole can be surely provided in the tape cassette, even if the tape cassette is miniaturized.