Abstract: A lock mechanism for disk drives includes a case slightly shorter than an ordinary diskette, a lock slantly disposed in front of the case and controlled by a key, a transmission shaft extending into the case and being moved forward when the lock is locked, and a hook member pivotally connected to the transmission shaft at the end extending into the case. The case has two spring clips separately accommodated in two recesses formed at two front corners of the case and are clamped by an upper and a lower link of a linkage which connects to and moves together with the transmission shaft. When the case has been pushed into a disk drive via a disk slot, the forward movement of the transmission shaft and the linkage allows the spring clips to spring open and push against the front inner wall of the disk slot of the disk drive. The backward movement of the transmission shaft and the linkage allows the spring clips to be pressed closed, permitting the case to be freely inserted into or drawn out of the disk drive.