To provide a pin tumbler lock which can use the second key rotatable in only one direction besides an ordinary key rotatable both right and left.

A middle ring 3 with a plurality of pin holes is rotatably provided between a large diameter part 21 of a lock shaft and a fixed cylinder 4, and an engaging projection 3a and an engaging recessed part 4a are provided between the cylinder 4 and the ring 3, and the ring 3 is mutually engaged so as to be rotatable within a fixed angular range. A middle cord pin 6 is slidably inserted in a pin hole inside the middle ring. When the first key is inserted in a key inserting hole, a face between a tip cord pin 5 and the middle cord pin 6 coincides with the rotary face between the large diameter part 21 and a middle ring 3, and the lock shaft 2 becomes rotatable with the key both right and left, and when the second key is inserted in the key inserting hole, the tip cord pin 5 enters between the large diameter part 21 and the middle ring 3 and joins them, and a face between the middle cord pin 6 and a drive pin 7 coincides with a rotary face between the ring 3 and the fixed cylinder 4, and the lock shaft 2 can therefore rotate in only one direction with the middle ring 3.