A tape cassette for a recording/reproducing apparatus comprises a cassette casing comprising an upper half and a lower half, a front cover provided to cover a front opening portion of the cassette casing for protecting a magnetic tape and for opening and closing the front opening portion and a locking member provided on at least one of right and left side surfaces of the cassette casing to lock the front cover when it is closed. A gap is formed between an outer side surface of the cassette casing and an inner side surface of the front cover so as to permit insertion of a member which serves to release the locking member from being locked. A projection is formed on an inner surface of the front cover covering the gap.