A device is capable of locking or unlocking a card in a card reader. An actuator carries a drive bushing onto which one end of a coil spring is mounted such that the axis of the coil spring is approximately parallel to the rotation axis of the actuator. The opposite end of the coil spring is mounted on a drive nut. A threaded shaft is fixed to a slide block with an elongated hole, and the movements of both are constrained to a single degree of freedom by the engagement of the elongated hole with a fixed pin and by the engagement of an extension of the threaded shaft with the inner hole of the drive bushing. The linear movement of the slide block causes a latch plate to move by means of a linear sliding pair between them so as to lock or unlock the inserted card.