PURPOSE: To reinforce a burglarproof function simply and easily without changing an existing door knob, which can be locked.

CONSTITUTION: Key-hole cover sections 2 are formed in front of a door knob body l while the front and rear places of the key-hole cover sections 2 are displaced. Cover fixing sections 3 are mounted at the rear of the door knob cover body 1. A notch 7 is formed to the door knob body among the key-hole cover sections 2 and the cover fixing sections 3, and the mechanism fixing arc 4 of opening and closing is formed. Locking sections 6, to which holes 5 for locking are bored, are set up on the outside at the rear of the door-knob cover body 1.