Disclosed is a rotary lock cylinder comprising a blocking element (25, 64) that engages into the rotor (10) in a closed position while releasing the rotor (10) in an open position. An actuator (17, 78) can be controlled in accordance with data located on the key (2). In order to displace the blocking element (25, 64) from the closed position into the open position, a latch element (33, 63) is provided which can be moved along with the key (2). The blocking element (25, 64) can be attached by means of the actuator (17). The energy required for moving the blocking element (25) is supplied by the user when introducing the key (2) into the key duct (11) such that the load on the power source used for actuating the actuator (17, 78) is minimal.