Abstract: A lock cylinder set to a lock has an outer cylinder serving as a housing. In the outer cylinder, a first inner cylinder into which an electronic key is inserted and a second inner cylinder connected to a locking/unlocking mechanism of the lock are rotatably set. A connecting pin is movably held by the first inner cylinder to connect the first inner cylinder with the second inner cylinder when the pin advances. A connecting pin control mechanism advances the connecting pin to mechanically hold the advance state of the pin when a proper key is inserted and retreats the connecting pin when the key is extracted. The connecting pin control mechanism has a cam plate contacting the protrusion of the connecting pin. The connecting pin retreats when the cam plate tilts and advances when the cam member rises.