A cylinder lock has a cylinder lock holder with a rotor rotatably disposed therein. The rotor has a plurality of grooves, with a plurality of tumblers slidably disposed in the grooves. Holder grooves are provided in the cylinder lock holder for receiving the tumblers projecting out of the grooves of the rotor. The rotor is able to be rotated in the cylinder lock holder in response to the insertion of a key into the rotor by causing the tumblers to be retracted from the holder grooves. Rotation is disabled when the key is removed, the tumblers projecting back into the holder grooves under the action of a spring biasing the tumblers. The key is inserted through a plurality of key insertion holes in the tumblers. Tooth portions are formed at respective contact portions between the tumblers and the inner surface of the cylinder lock holder, the respective tooth portions being engaged with each other when the key is removed from the lock.