Abstract: A locking device is disclosed which comprises a multi-leaved key which is adapted to be inserted within a correspondingly configured keyhole provided within an inner cylinder member. The inner cylinder member is slidably disposed within an outer cylinder member so as to permit or prevent rotation of the inner cylinder member with respect to the outer cylinder member through the interaction between a projection member and a slot or groove respectively provided upon the inner and outer cylinder members, as well as to permit or prevent the inner cylinder member from being engaged with a cam member which is operatively associated wih a lock bolt.