PURPOSE: To prevent unlocking by unjust means by a method in which the projecting amount of a lock part is differentiated according to the height of a key corresponding to the contact part of a tumbler, and the contact faces of each key are allowed to align at the same levels regardless of the projecting amounts.

CONSTITUTION: In a rotor 2, tumblers 13 are provided according to the height of the key top 6a corresponding to each contact part 13c, and according to the positions, the projecting amount A of the lock part 13b is differentiated. The lock parts of smaller projecting amount A are provided in high key hole 14 position, and also ones of greater projecting amount A are provided in low key hole position. When the lock parts 13b are projected, the contact faces 14a of each key are allowed to align at the same levels regardless of the projecting amounts A. In a state that the key is drawn out, the height of the tumbler 13 is read to make the production of master key impossible. The safety of the cylinder lock can thus be raised to prevent unlocking by unjust means.