PURPOSE: To improve burglarproof property by a method wherein a key cylinder is provided above a guard bar bracket fixed to a door inner panel and the key cylinder is supported by first and second extensions provided above the bracket.

CONSTITUTION: When a key cylinder 2 is forced in a direction F, the cylinder 2 oscillates to unlock a lock device of a door 9. Then a first extension 12b of a guard bar bracket 12 makes contact with a cylinder inside end 2b, and hence large oscillation of the cylinder 2 is prevented, thereby preventing wrong unlocking. When the cylinder 2 is turned in a direction G, a control bar 8 is lowered to unlock the lock device of the door 9. In this case, a retainer clip 3 also is turned together with the cylinder 2 so that a retainer 3a makes contact with a second extension 12c of the bracket 12 to prevent large oscillation of the cylinder 2, thereby preventing wrong unlocking. Consequently, burglarproof property can be ensured without increasing number of parts.