Said lock core has a column core (10) which contains, in longitudinal shift mode, sheet rotors (30) for bearing spring force (14). A key having a certain longitudinal cross-section is used for offsetting these sheet rotors (30) at their controlling sides (36) for a specified altitude. The column core (10) and the sheet rotors (30) ate received in a lock core case (20) which has a locking hole (21) and an opposing prevention hole (22). When the key is pulled out, the sheet rotors (30) insert an end-face (38) thereof into the locking hole (21). And in used situation, when a true or a fake key is inserted-in or pulled-out, the rotors (30) move the terminal edges (39) to the prevention hole (22) temporarily. In order to obtain a volume-saved structure in the lock core, it is proposed that theterminal edges (38, 39) of the rotors (30) is evenly constituted, relative to the radius (18) of the column core.