To provide a burglar preventing device whose assembly is easy.

A detection part 24 which electrically detect the inhibition of the ringing operation of a buzzer 21 is installed in a burglar preventing device main body 11. A magnet 37 for releasing the restraint of a slider 13 and the inhibition part 23 of an informing operation inhibiting the ringing operation of the buzzer 21 are installed in a releasing key 12. When the releasing key 12 is brought close to the prescribed position of the burglar preventing device main body 11, the restraint of the slider 13 is released and the ringing of the buzzer 21 is inhibited by an electric signal. Thus, structure whose assembly is easy is provided.