To provide a composite disc tumbler lock capable of miniaturizing a cylinder lock.

The composite disc tumbler lock comprises an outer cylinder 1 in which a cam groove 2 is formed along a bus bar of an inner peripheral surface, an inner cylinder 3 rotatably fitted to the outer cylinder 1 and provided with a key hole 4 opened along a center axis, and a locking bar 6 extending along the bus bar of the inner cylinder 3 and guided to be movable in the radial direction at an outer peripheral part of the inner cylinder. An outside edge of the locking bar 6 is urged to project outward in the direction to be engaged with the cam groove 2. A disc tumbler 9 having a key insertion hole 11 capable of surrounding a key hole 4 is longitudinally movably housed in each of a plurality of slots 8, 8 arranged along the center axis of the inner cylinder 3. An unlocking cutout 13 is formed in an end edge of the side facing the locking bar 6 of the disc tumbler 9 so that the unlocking cutout of each disc tumbler may interface with the locking bar 6 when a duplicate key 5 is inserted into the key hole.