A connection lock capable of executing locking operation without keys includes a case to house an actuation mechanism, a rotary cylinder and an elastic element. The actuation mechanism includes a movable leg and a fixed leg. The movable leg is moved by the elastic element to be close to the fixed leg at an unlocking position in normal conditions. The rotary cylinder has a nudging member extended from the front end that can move the movable leg away from the fixed leg at a locking position. The case has a one-way hump corresponding to the rotary cylinder to allow the rotary cylinder to be turned in one way to switch the movable leg from the unlocking position close to the fixed leg and to the extended and locking position.