To provide a double lock capable of reducing the risk of being unlocked fraudulently without requiring the user to make complicated operation by employing two locks of a reverse turning structure operated by using the same key and turned reversely to each other and interlocking the two locks with each other to restrict their mutual movement to fix the operation sequence of the two keys.

The double lock comprises a first lock 10 and a second lock 20 respectively having cylinders 11, 21 capable of being locked and unlocked by using the same key but turned in the mutually opposite directions, a first control rod 13 interlocked with turning of the cylinder 11 of the first lock, retaining the cylinder 21 of the second lock to inhibit its turn when being locked and permitting the cylinder 21 of the second lock to turn when being locked and a second control rod 23 interlocked with turning of the cylinder 21 of the second lock to permit the cylinder 11 of the first lock to turn when being unlocked and retaining the cylinder 11 of the first lock to inhibit its turn when being locked.