To provide a composite door lock preventing picking crime by combining two cylinder locks to enhance crime prevention effect.

The composite door lock is constituted of a first dead bolt 5 interlocking with a first cylinder 2 built-in in a door 1 and retractably fitting to a support seat 11 provided in a door frame 10, a second cylinder 4 provided in the vicinity of the dead bolt, and a second dead bolt 12 interlocking with the second cylinder lock 4 and fitting to the first dead bolt 5 to be vertically retractable. By locking the second cylinder 4 in the condition that the first cylinder lock 2 is locked, the second dead bolt 12 is fitted to the first dead bolt 5 to lock it.