To provide a compound disk tumbler lock capable of miniaturizing a cylinder lock.

In this compound disk tumbler lock formed by compounding a disk tumbler and a lever tumbler, the disk tumbler is extracted from at least one selected slot 8, and instead an idle disk tumbler 21 having the same configuration as the extracted disk tumbler is stored. In this idle disk tumbler 21, when an engagement projection is engaged with an idle recess formed on a side edge corresponding to a duplicate key, a release cutout 13 is aligned with the inner edge of a locking bar 6, and the depth of the idle recess is set to a value different from any depth of a recess set in the extracted disk tumbler, including zero.