To provide a crime prevention device capable of preventing an intruder from opening a lock part simply even if window glass or the like is broken.

This crime prevention device installed close to the lock part includes a movable part (each of right and left arm parts constituted by an upper arm 4, a lower arm 5, a lens cap 6, and a sensor substrate 7) and a lock releasing part (a lock releasing switch 9). This crime prevention device can take a first state in which opening of the lock part is not prevented (the state in which the arm part is closed) and a second state in which opening of the lock part is prevented (the state in which the arm part is opened) depending on travel of the movable part. This device cannot shift to the first state from the second state unless locking is released by the lock releasing part.