To take a measure of preventing a cylinder 2 from slipping out from an outer 1 in a cylinder lock because the locking pin of a conventional cylinder lock, which is arranged extendedly from the pin insert hole of the outer 1 to the pin sliding groove of the cylinder 2, is often dropped out from the pin sliding groove, causing the drop out of the cylinder 2 from the outer 1.

The locking pin 5 is driven to a pin receiving hole provided on the side surface of the cylinder, the end part of the locking pin 5 is protruded from a through elliptic hole 14 provided on the side surface of the outer 1, whereby the cylinder 2 is rotatable within the longitudinal range of the hole 14 relative to the circumferential direction, and prevented from moving relative to the axial direction because the locking pin 5 abuts on the inside surface of the hole 14. Accordingly, the drop out of the cylinder 2 from the outer 1 can be prevented. Since the locking pin 5 is surely fixed to the pin receiving hole, the drop out or floating of the pin 5 as in the past can be prevented.