Abstract: A pickproof cylinder lock has a plurality of key-actuatable spring-tensioned pin tumblers wholly received in the cylinder and slidably mounted therein, and a ball connected with each pin to be raised or lowered with the pin. The balls are normally held in inactive positions by their pins, but when a proper key is inserted, the balls are brought into active positions by their pins and form a straight link through which key actuation of the pins is translated into a force on a lock-operating member to move the same to a lock-open position. A spring member normally locks the lock-operating member rigidly in a lock-closed position, and the force produced by the balls in their active position is also directed against the spring member to move the latter to a position in which it releases the lock-operating member.