To provide a picking preventing cover, which enables anyone to simply fit the cover to a door and open or close a key with one hand without removing the cover and is adaptable to a one-door two-lock system.

The key 3 having a key lever 2 on the inside of a case 1 is provided on the upper face of the case 1, and the cover 5 having an arm lever 4 on the inside of the case 1 is provided on the front face of the case 1. Recesses 8 each having a recess opening section 7 are provided on an upper opening section 6 and a side face of the case 1, and a bolt 9 is provided on each recess 8.